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The Brazilian petroleum and chemical industry had basically used medium-voltage (MV) power assemblies based on ANSI/NEMA for many years. However, in the last three decades, due to the Brazilian Standard Association orientation, the users and manufacturers have been changing their philosophies to the IEC culture. As there has been an everyday increase in the opportunity and also in the need of MV electrical power distribution in petrochemical facilities, there is the chance of adopting an MV switchgear or controlgear design based on ANSI or IEC standards, according to each plant specifications. Although the use and design of MV assemblies are based on the electric power system needs and characteristics, they are also a result of the current scenario and experience of a specific petrochemical facility. Since both ANSI and IEC universes have strong experience, knowledge, and huge safety concerns in electrical equipment design and application, the final choice is an interesting decision. It is important to keep in mind that the use of MV assemblies has to face technical and safety key issues as they are connected to an industrial power system, and both ANSI and IEC deal with such requirements very carefully: each one in its own way. This paper deals with impacting topics related to MV switchgear and controlgear such as the following: 1) ANSI and IEC requirements; 2) rated values and characteristics; 3) ancillary and power equipment application; 4) safety; and 5) ergonomics.

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Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

Luiz Felipe O. Costa

Senior Member, IEEE

Eaton

Estellito Rangel Jr.

Senior Member, IEEE

Petrobras

José M. de Carvalho Fo.

D.Sc.- E.E.

UNIFEI - GEQEE

Rogério C. Barros

Member, IEEE

Eaton

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Identifier: 10.1109/

PCICon.2013.6666014

Abstract

The Brazilian petroleum and chemical industry has

used MV power assemblies based on ANSI/NEMA姞

for many years. However, in the last three decades,

due to the Brazilian Standards Association's

orientation, users and manufacturers have been

changing their philosophies to the IEC culture.

Because of both the increasing opportunity and

the need for medium voltage electrical power

distribution in petrochemical facilities, there is an

opportunity to adopt MV switchgear or controlgear

design based on ANSI or IEC standards, according

to each plant's specifications. Although the use and

design of MV assemblies are based on the electric

power system's needs and characteristics, they

are also a compromise with the current scenario

and experience of a specific petrochemical facility.

Because both ANSI and IEC universes have strong

experiences, knowledge, and huge safety concerns

in electrical equipment design and applications, the

final choice is interesting.

It is important to keep in mind that MV assemblies

have to face key technical and safety issues

because they are connected to an industrial power

system, and both ANSI and IEC deal with such

requirements very carefully. This paper deals with

impacting topics related to MV switchgear and

controlgear such as:

• ANSI and IEC requirements

• Rated values and characteristics

• Ancillary and power equipment applications

• Safety

• Ergonomics

Introduction

In the Brazilian electrical sector, the 20th century

saw a mix of influences from North America

(U.S. and Canada) and Europe (mainly Germany,

England, France, and Italy). The petrochemical

segment and electrical power distribution

industry were driven primarily by ANSI and

NEMA. In fact, when the Brazilian government

decided that it needed to unify all frequency

values in the country, the adopted value was

60 Hz, even with strong impacts in generation

and distribution sectors of very important areas,

such as the state of Rio de Janeiro, where the

main utility company's system had 50 Hz as its

rated frequency. The decade of the 1960s was a

challenging time for Brazilian electrical engineers

and technicians.

Another key milestone in Brazilian electrical history

was the government's decision to embrace the

adoption of ISO/IEC standards and guidelines for

the national technical universe. This decision drove

ABNT (Associação Brasileira de Normas Técnicas)

to adopt IEC standards as the main reference

for Brazilian Technical Standards (such changing

movements increased by the end of the 1970s—

an example of this important change at that time

was the adoption of squared millimeter values to

substitute AWG/MCM scales for copper wires and

cables). Since then, other changes have occurred

in our electro-technical culture. In the last two

decades, all related switchgear and controlgear

standards moved closed to the IEC culture (there

were situations where the related technical

committees decided to translate the original IEC

standards—significant examples are related to

LV and HV switchgear and controlgear families).

An electric installation itself and its distribution

and control equipment are classified primarily

by their rated voltages. In the IEC culture, we

have the so-called low and high voltage ranges.

Also, according the IEC, the threshold between

the two ranges in AC installations is 1000V (rms

value). However, it is normal in the ANSI universe

of electrical distribution companies and several

industry segments to refer to electric power

installations and equipment for voltages up to 38

kV as "MV" (medium voltage) systems. We will

keep our discussion and analysis for applications

between 2.4 and 34.5 kV.

The Brazilian electrical culture considers AC

(60 Hz) voltages values to be from 1 to 38 kV

(rms values) as in the medium voltage (MV) range,

due to our strong ANSI heritage in the electrical

power distribution and petrochemical sectors.

White Paper WP022001EN IEEE November 2013

Effective June 2015

Supersedes February 2014

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IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

Within this context, switchgear and controlgear assemblies, such as

motor control centers (MCC) and power distribution centers (PDC),

have been used to supply, distribute, and control MV electrical power.

Most of the time, these assemblies are installed in locations where

special requirements or conditions can be found, and all related

phases of equipment lifetime demand careful attention.

As is known, a failure in an assembly results in multiple disorders

and considerable costs. Because of this, a strong knowledge of

switchgear and controlgear assemblies increases the probability

of safeguarding the installations and personnel. Therefore, it is

necessary to provide clear guidelines and powerful tools for the

professionals in charge of specifying and/or dealing with switchgear

and controlgear assemblies.

Figure 1. Example of an ANSI/NEMA Assembly

Figure 2. Example of an IEC Assembly

Figure 3. Part of a Single-Line Diagram of a Petrochemical Unit

Figure 4. MV Switchgear Assembly Corresponding to the

Single-Line Diagram Shown in Figure 3

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Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

Analysis and discussion

Following the aforementioned scenarios, we need to keep in mind

that all electrical power in an MV industrial installation should be:

• Operated

• Protected

• Controlled

• Regulated

• Measured

Such situations can be achieved directly by MV switchgear and

controlgear assemblies with associated components, enclosures,

interconnections, and accessories. Always take into account a safe

operation and the condition of the electrical system and equipment,

and keep in mind that the highest priority is always the person.

Independently of which philosophy is adopted, an MV interrupter unit

will incorporate some basic components inside the compartments

of a metal-enclosed column such as the power circuit breaker, CTs,

protective relays, busbars, and so on.

It is possible to define the main compartments and parts of an MV

metal-enclosed air-insulated indoor assembly (see Figure 5 and

Figure 8). They are:

1. LV compartment (control)

2. Dynamic flaps (overpressure relief)

3. Main busbar compartment

4. Interrupting device (MVCB) compartment

5. Withdrawable circuit breaker

6. Current transformers (CTs)

7. Power cables compartment

8. Earthing switching (grounding device)

9. Automatic shutters

Because all concerned physical and chemical phenomena are the

key bases for any technical approach, no matter which standard is

adopted, we must understand the real needs of the customers and

their installations.

Our analysis will focus on the following topics.

ANSI/IEEE C37.20.2

In its scope, the standard ANSI/IEEE姞 C37.20.2 [1] establishes

its aim to cover metal-clad (MC) switchgear and its devices and

equipment. This standard is concerned with enclosed, indoor, and

outdoor switchgear assemblies rated more than 1000 Vac. This

document is normally adopted in the U.S.

This standard has certain unique requirements, such as insulated

busbars and connections, withdrawable main switching devices, and

minimum thickness for covers, barriers, panels, doors, and so on.

During the last three decades, we saw an increased use of two-high

(double-tier) configurations for metal-enclosed column construction.

This approach has proven its effectiveness. Its appeal is so strong

that the main MV metal-clad switchgear manufacturers in the U.S.

have this type of structure in their portfolios.

Figure 5. Two-High (Double-Tier) ANSI MV Assembly

View A View B

Figure 6. Typical ANSI Metal-Clad Compartment for Circuit

Breaker. View A: Metallic Shutters Closed. View B: Shutters

Open, Showing the Spouts' Power Connections and LV Ring

Type CT (Mounted over the Bushings)

Front View Back View

Figure 7. Front and Back Views of a Typical ANSI MV Vacuum

Circuit Breaker

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Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

IEC 62271-200

The IEC 62271-200 [2] standard establishes the requirements for

factory-assembled switchgear and controlgear assemblies with an

externally grounded metal enclosure for AC systems (50 or 60 Hz)

with operating voltages in the MV range (above 1 kV and up to and

including 52 kV). This is an international standard that is normally

used in Europe and also as a reference in several countries around

the world.

In order to work with this standard, it is necessary to reference the

document IEC 62271--1 [3].

Depending on the application, it will also be necessary to consult

other IEC standards such as:

• IEC62271-100 (high voltage AC circuit breakers) [4]

• IEC62271-102 (high voltage AC disconnectors and

earthing switches) [5]

• IEC62271-106 (high voltage AC contactors) [6]

• IEC60529 (IP degrees provided by enclosures) [7]

• IEC60044-1 (instrument transformers—CTs) [8]

• IEC60044-2 (instrument transformers—inductive VTs [9]

• IEC60282 (high voltage CL fuses) [10]

Today, the more common constructing approach in the IEC universe

is the so-called "mid-high" (single-tier) configuration for metal-

enclosed column constructions. It is an evolution of the classic

European design with one roll-on circuit breaker per column.

Such evolution was based on the idea of front access for cable

connections, making it possible to mount a line up with its back

side close to a wall in order to reduce the area necessary for

equipment erection.

Figure 8. Typical Mid-High (Single-Tier) IEC MV Assembly

View A View B

Figure 9. Typical IEC Metal-Enclosed Compartment for Circuit

Breaker. View A: Shutters Closed. View B: Shutters Open,

Showing the Spouts' Power Connections

Figure 10. Front and Back Views of a Typical IEC MV Vacuum

Circuit Breaker

ABNT NBR IEC 62271-200

The current Brazilian standard ABNT NBR IEC 62271-200 [11] for

MV metal-enclosed switchgear and controlgear is based strongly

on the original IEC document. Because of this, the ABNT reference

code uses the original IEC number that deals with metal-enclosed

assemblies for voltages above 1 kV and up to and including 52 kV.

It replaces the old NBR 6979 standard [12], which already included

many IEC features in its text.

Basic required characteristics of MV switchgear and

controlgear assemblies

The use and application of MV metal-enclosed assemblies

are driven by the following characteristics, described in the

aforementioned standards:

• Rated voltage

• Rated insulation level (lightning impulse and power frequency

withstand voltages)

• Rated frequency

• Rated current

• Rated short-time withstand current

• Peak withstand current

• Duration of short-circuit

• Internal components rated values

• Fluid level and/or pressure

In order to help to understand the way that the Brazilian

petrochemical industry has dealt with the transition from one

standard's approach to another, it will be helpful to analyze each

of topics mentioned above.

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Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

Rated voltage (Ur)

Because of ANSI/NEMA influence, the most common operating

voltage (Ue ) values adopted at MV levels in the Brazilian oil and

gas segments are 4.15 and 13.8 kV. Other than these values, it is

possible to find other common NEMA values: 2.4 and 34.5 kV. The

former has been abandoned in new industrial applications, while

the latter has increased its presence recently. It is also possible

to find operating voltage values like 3.3 and 6.6 kV, but they are

uncommon and would only be found in very few applications in the

petrochemical segment in Brazil.

Table 1. Rated Voltage and Insulation Levels

BR ANSI/NEMA IEC

abbbccc

Ue [kV] d Ur [kV] e Ud [kV] f Up [kV] g Ur [kV] e Ud [kV] f Up [kV] g

[2.4] 4.76 19 60 3.6 10 40

[3.3] 4.76 19 60 3.6 10 40

4.16 4.76 19 60 7.2 20 60

[6.6] 8.25 36 95 7.2 20 60

[11.0] 15 36 95 12.0 28 75

13.8 15 36 95 17.5 38 95

[23.0] 27 60 125 24.0 50 125

34.5 38 80 150 36.0 70 170

a Column 1: normal operating voltages in Brazil. The values in brackets are uncommon in the

petrochemical sector.

b Columns 2/3/4: related to ANSI (IEEE Std 20.2-1999—Table 1) and also to IEC 62271-1—Table 1b.

c Columns 5/6/7: related to IEC 62271-1–Table 1a.

d Ue : operating voltage (kV–rms value).

e Ur : rated voltage (kV–rms value).

f Ud : rated power frequency withstand voltage (kV–rms value).

g Up : rated lightning impulse withstand voltage–BIL (kV–peak value).

The current Brazilian practice is to associate the 4.16 and 13.8 kV

values to the rated voltages (Ur ) of 7.2 and 17.5 kV from Table 1a

from IEC 62271-1: 2007: "rated insulation levels for rated voltages

of range I, series I (rms value for rated voltage—Ur )." Such choice,

without the knowledge of the entire Brazilian electrical sector, is

not considered to be the best, because the same standard offers

another list with values closer to ANSI/NEMA culture (Table 1b).

However, in this case, it was more of a political decision based on

a rational technical reason: the federal government's orientation to

embrace the International System of Units (SI) in 1962 (reinforced by

a government decision of 1988) and the widespread participation in

several segments of the Brazilian economy of important companies

with IEC-based knowledge.

Rated insulation level (Ud /Up)

Keeping the analysis of 4.16 and 13.8 kV values as operating voltages,

it is evident that the required values of 20 and 38 kV, as power

frequency withstand voltages (for rated voltages of 7.2 and 17.5 kV,

respectively) did not have any significant impacts. These new values

are very close to the old required values of 19 and 36 kV for power

frequency withstand voltages (ANSI/NEMA practice). The rated

lightning impulse withstand voltage (Up ) values are the same for

both cultures (ANSI and IEC): 60 and 95 kV (peak values).

Figure 11. Internal MV Switchgear Configuration Tested for

95 kV BIL (See Oscillograms on Figure 12)

The procedural differences regarding the test verification of lightning

impulse (BIL—Basic Impulse Level) caused some confusion in the

beginning stages of the change from ANSI to IEC. Although the

standard wavef orm criteria (1.2 x 50 μs full wave) are the same

for both cultures, the differences in the number of positive and

negative wave applications created some confusion. The "15 x 2"

test procedure (15 applications with a maximum of two flashovers in

self-restoring isolation parts) for each polarity (discharge probability

of 13.3%) is more demanding when compared to the old ANSI

practice for BIL verification of "3 x 1 x 3" (total of six applications

with one flashover in the first three) for each polarity (probability

of 16.7%). The first movement of end users and some consulting

engineers was to ask for a new BIL test in the case of equipment

based on the old ANSI requirement. When ANSI adopted the new

and more demanding acceptance criteria of the "3 x 1 x 9" test (one

flashover in the first three demands nine more shots, for a total of

12 applications—8.3% probability), such retest requirements were

finally abandoned.

Figure 12. Oscillograms of 15 Positive and 15 Negative Voltage

Wave Applications of Lightning Impulses

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Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

Rated frequency (fr)

The current adopted rated frequency value in Brazil is 60 Hz.

Although this is the standard value for the ANSI/NEMA universe,

this is also an IEC recognized value.

Rated normal current (Ir) and temperature rise

The difference between ANSI values (1200/2000/3000A) and

IEC values (1250/2000/3150A) is not significant. The adoption of

multiples from R10 series, as specified in IEC 62271-1, -200, and

60059 [6], occurred immediately and without any significant impact.

Table 2. Typical Values for Rated Continuous Current

ANSI IEC

ab

AA

630

800

1200 1250

1600

2000 2000

2500

3000

a Column 1: continuous current ratings according to sub-section "5.4.2" from ANSI/IEEE Std 20.2-1999.

bColumn 2: rated normal current (Ir) according to sub-section "4.4.1" from IEC 62271-200.

The R10 series (1/1.25/1.6/2/2.5/3.15/4/5/6.3/8) is part of a system of

preferred numbers for use with the ISO metric system, proposed in

1870 by Charles Renard (1847–1905), a French military engineer.

One interesting occurrence during the transition from ANSI to IEC

proposed values for rated current was that the higher temperature

rise values for silver-coated connections promoted a comfortable

perception by end users. This can be explained by the following

equations relating the temperature rise to the current level:

The indicated terms are:

•I r : rated current value

•I e : operating current value

•∆y r : rated temperature rise

•∆y e : operating temperature rise

As an example for this specific point, let's see what could happen

when the equation is applied to a 3150A current in a 3000A ANSI

metal-clad busbar with silver-plated connections. Based on [1], the

following relation applies:

The result of this equation is approximately 72°C. It represents

the temperature rise for a 3150A current applied to a 3000A ANSI

switchgear. In other words, the equipment is able to accomplish

the IEC requirement for a maximum temperature rise of 75°C

(see Table 3) for a silver-coated connection.

In the case of the comparison of the 1200A used at the 1250A level,

the value for temperature rise would be approximately 71°C.

The same conditions are considered for the previously mentioned

3000A structure.

Table 3. Limits of Temperature Rise

ANSI IEC

a bbcc

Bus

Connection

or Cable

Termination

Temperature

Rise

°C

Total

Temperature

°C

Temperature

Rise

°C

Total

Temperature

°C

Bare copper 30 70 50 90

Tin-coated 65 105 65 105

Silver-coated 65 105 75 115

Nickel-coated — — 75 115

Cable to copper 30 70 50 90

Cable to tin 45 85 65 105

Cable to silver 45 85 65 105

aColumn 1: types of bus or connection (bar-to-bar or bar-to-cable).

bColumns 2/3: temperature limits (rise and maximum total values) according to ANSI/IEEE

Std 20.2-1999–Table 3.

cColumns 4/5: temperature limits (rise and maximum total values) according to IEC 62271-1–Table 3.

Although the combination of hot and humid conditions with a

sulfur rich environment on the copper (Cu—base metal) and silver

(Ag—plating) elements used as contact surfaces in certain industrial

atmospheres results in a well-known impact, it has not been a

concern in the main petrochemical plants in Brazil. The well-known

process of corrosion of Cu and Ag, under the conditions described

above in refineries, petrochemical plants, paper and pulp facilities,

steel mills, and wastewater unites has not been reported as a

critical issue in the Brazilian oil and gas segments. It is possible that

this is because there is a strong tendency to apply air conditioning

units, filters, and pressurized systems in the main electrical

rooms together with the criteria of installing the switchgears and

controlgear assemblies as far away as possible from the main

concentration of sulfur fumes (hydrogen sulfide). As clarification,

the authors have already seen the requirement of using nickel (Ni)

as plating material over copper in specific areas of steel mills and

pulp and paper facilities in Brazil.

Rated short-time withstand current (Ik) and CB short-circuit

interrupting capacity

The ANSI decision to adopt 1.0 as the rated value for the "K-factor"

helped to reduce the doubts and confusions that were still noted

among many Brazilian designers. Although the ANSI/NEMA

philosophy had a strong influence in the Brazilian industry for several

years, it was possible to see many doubts related to the use of

K-factor, the relation between Isc and system operational voltage, and

MVA SC capacity concepts. It was common to see designers claiming

that a "500 MVA" / 15 kV circuit breaker should be able to handle a

20.9 kA (symmetrical RMS) at 13.8 kV, based on the relation:

Here, the terms are:

•I SC : short-circuit current (kA–rms value)

•MVA_SC: three-phase circuit breaker interrupting capacity (MVA)

•U e : operating phase-to-phase voltage (kV)

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Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

This approach is incorrect; it is a misunderstanding of the old MVA

classification for MV circuit breakers (such a circuit breaker is

sometimes still referred to as a 500 MVA class, and this normally

leads to an incorrect analysis). It is completely against the ANSI

guidelines for such applications.

The Voltage Range Factor (K-factor) was established to take

advantage of the characteristics of circuit breakers with interrupting

technologies, such as oil and air, to increase their SC capacities as

the system voltage decreases. However, with new technologies

such as SF6 and vacuum as interrupting medium, the specialists

found that reducing the operating voltages would not improve the

circuit breaker interrupting capacity.

According to [19], the Rated Voltage Range Factor (K) defines the

voltage range where the value of the symmetrical interrupting

current (rms value) varies inversely with the operating voltage at

the point of circuit breaker application. Also, the rated symmetrical

short-circuit current (Rated Isc ) is defined for the rated maximum

voltage (Ur ). So, the maximum symmetrical short-circuit current at

the minimum operating voltage (minimum Ue ) is given by:

Here, the terms are:

• Max_I SC : maximum symmetrical short-circuit current capability at

the minimum operating voltage (kA–rms value)

• Rated I SC : rated symmetrical short-circuit current (kA–rms value)

• K: rated voltage range factor

In the cases where the values of K are greater than 1.0, the

symmetrical interrupting capability between rated maximum

voltage and 1/K times the rated maximum voltage is defined as:

Here, the terms are:

• I Ue : symmetrical short-circuit current capability at operating

voltage (kA–rms value)

• Rated I SC : rated symmetrical short-circuit current (kA–rms value)

• U r : rated maximum voltage (kV)

• U e : operating voltage (kV)

According to [4], for a circuit breaker with a value of 18 kA for

the rated symmetrical short-circuit current, at a rated maximum

voltage of 15 kV, we, in fact, have 19.6 kA as the symmetrical SC,

as seen below:

The use of a list based on the R10 series to choose the best value

for the symmetrical short-circuit current in a context of maximum

system voltage, which is in line with the new ANSI concept of

"K-factor=1.0" , simplified the task for many professionals.

Table 4. Rated Short-Circuit Current for a 15 kV System

Short-Circuit Level ANSI IEC

a bcde

MVA kA rms K-Factor kA rms K-Factor

500 18 1.3 20 1.0

500 18 1.3 25 1.0

750 28 1.3 31.5 1.0

1000 37 1.3 40 1.0

1000 37 1.3 50 1.0

a Column 1: although it has not been a standard practice for a long time, the MVA values are shown

here as informative values to be used just as reference.

b Column 2: rated rms value for the symmetrical short-circuit current in the maximum voltage (15 kV).

c Column 3: proposed K-factor for a range of current based on voltage limits (maximum and minimum

values) for an inverse relation between SC current (symmetrical RMS value) and operating voltage.

d Column 4: rms value for the symmetrical component of SC current, based on the IEC practice

(R10 series).

e Column 5: theoretical value for K-factor at the maximum voltage of 17.5 kV (in fact, current ANSI

practice is k=1.0 for such level of voltage).

Rated peak withstand current (Ip)

The peak instantaneous value of the first half-cycle of the rated

withstand current for an MV switchgear and controlgear assembly

is based on the relation between itself and the effective value of

the short-circuit symmetric component. Thanks to the harmonization

process between ANSI and IEC for MV and HV circuit breakers, the

current adopted value for X/R ratio is 17, that is the product of the

time constant (π), 45 ms, and the angular speed (v) of a system with

frequency of 60 Hz, as follows:

As already mentioned, this practice drives to the use of a value of

2.6 for the ratio of the peak current to its rms value for the first

half-cycle of SC current (see IEC 60909 [14] for the mathematical

relations among the X/R value, the effective value of symmetric

component of SC current, Ik '', and the peak instantaneous value

of the first half cycle, ip ). This approach allowed the designers to

eliminate the old conflict between 2.5 (IEC proposed value) and

2.7 (old ANSI over conservative value), so there was no significant

impact in terms of application and selection of MV gear:

8

Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

Rated duration of short-circuit (tk)

The decision of ANSI to reduce the rated value from 3 seconds to

2 seconds did not represent any impact in design criteria. In fact,

the IEC value of 1 second had already been used for a long time. We

could say that ANSI and NEMA's strong performance in this topic

could represent a difference in some very specific cases.

Regarding the last two topics of our previous list of rated

characteristics, we can say that there were no significant impacts

in the way that the Brazilian oil and gas market sees the needs for

critical items of MV switchgear.

Constructive designs and safety philosophies of

MV switchgear assemblies

The main reasons behind the adoption of enclosures for

MV switchgear assemblies are the provision of protection of:

• Persons against electric shock

• Persons against arc-flash risks related to the presence of

incident energy

• Equipment against ingress of solid foreign objects

• Equipment against harmful effects from the ingress of water

In the Brazilian petrochemical industry, steel is used as the material

for the enclosures of MV assemblies. During many years, the main

classification used for switchgear assemblies was based on IEEE

definitions for metal-enclosed power switchgear (a switchgear

assembly completely enclosed on all sides and on top with sheet

metal, containing primary power devices and possibly including

control and auxiliary devices, segregated from MV conductors and

structures by grounded sheet metal). The old Brazilian classification

of MV assemblies was basically composed of two types: metal-clad

[1] and metal-enclosed interrupter [22] (normally referred to only as

"metal-enclosed" type).

An ANSI/IEEE metal-clad switchgear is characterized by:

• The main device is of drawout type

• Major parts of the primary circuit are completely enclosed by

grounded metal barriers

• All live parts are enclosed within grounded metal compartments

• Automatic shutters for removable elements when they are in the

disconnected, test, or removed positions

• Primary conductors and connections are covered with

insulating materials

• Mechanical interlocks for proper operating sequence

• LV components and their wirings are isolated by grounded

metal barriers

I. LV Compartment

II. Main Busbar Compartment

III. Circuit Breaker Compartment

IV. Connection (Cables) Compartment

Figure 13. Compartments of a Typical Functional Unit

The third edition of IEC 60298 [18] defined three classes for a metal-

enclosed assembly:

• Metal-clad (different from ANSI/IEC definition)

• Compartmented

• Cubicle

Based on IEC 60298 [18], the IEC 62271-200 [2], in its "Annex C" ,

presents a table describing the comparison of IEC and IEEE [14]

definition of metal-clad switchgear.

Table 5. Comparison of ANSI and IEC

(Based on Annex "C" of IEC 62271-200: 2003)

Description ANSI IEC

abc

Reference IEEE C37.20.2 IEC 60298

Compartments

(power sections)

≥ 3 ≥ 3

Circuit breaker Withdrawable Fixed allowed

Conductors Covered by

insulating materials

Bare allowed

Barriers between vertical

sections for main bus

Need barriers per panel No requirement for barriers

VT d / CPT eDedicated compartment No specific requirement

VT d Withdrawable Fixed allowed

CPT e Fixed allowed but with

withdrawable fuses—

dedicated compartment

No specific requirement

CT f Presents a table with

standard CT accuracies

No specific requirement

a Column 1: construction characteristic or component.

b Column 2: ANSI requirements.

c Column 3: IEC requirements (based on the old IEC 60298 [8]).

d VT: voltage transformers.

e CPT: control power transformers.

f CT: current transformers.

9

Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

Since the release of the standard IEC 62271-200, there is a new

approach to classify the ways that a switchgear's builders can

segregate different compartments and maintain service continuity.

The LSC ("loss of service continuity") classification seeks to inform

the user how far the system continuity can be kept when accessing

any power (main) compartment: busbar section, cable connections,

and main switching device.

The category LSC2B allows for maximum continuity of service of

the system during access to any switchgear's compartment.

Another new classification is related to the type of material used as

a partition between compartments (including shutters): PM (metallic

partitions) or PI (insulation material). The PI also refers to situations

where just part of the partition or shutter is made of insulation-

covered parts. The use of a metallic partition is to avoid the presence

of any electric field in the opened compartment and to eliminate

any electric field change in the surrounding compartments (with the

exception of the effect of the shutter changing position).

Therefore, it is possible to say that ANSI metal-clad switchgear

would be classified as "LSC2B-PM" (metal-clad structure with

withdrawable circuit-breaker and metallic shutters).

Figure 14. Internal View of Typical Sections of an IEC

Metal-Enclosed Switchgear (No Barriers Between Sections,

nor Busbars Covered by Insulating Materials)

Figure 15. Examples of Main Bus Barrier for MV Switchgear and

Controlgear Assemblies

In this new scenario of IEC classification, the Brazilian users

decided to adopt the "LSC2B-PM" form. Besides this, because of

the reliable and safe performance for many years of switchgear with

ANSI-based designs, the customers also claim that any new line-up

for oil and gas segments should have the following requirements in

their construction:

• Dedicated interrupting (MVCB) compartment with a

withdrawable CB

• Metallic shutters (automatic type) and partitions

• Insulated busbars

• Withdrawable VT

• Dedicated main busbar compartment, segregated by

metallic partition

• Use of insulating bushings for buses penetrating metallic barriers

• Dedicated power cables compartment, segregated by barriers

The relatively new characteristic is the adoption of "Earthing

Switches" integrated into the power circuit instead of "Ground

and Testing Device" as we normally see in the ANSI culture. The

integration of an internally dedicated "earthing" (grounding) switch

drove the decision of switchgear designers to adopt "Voltage

Detection Systems" (a combination of capactive dividers and

indicating devices) to help the user identify the presence of voltage

in the cable compartment.

Key for numbers showed on the figure:

1. LV compartment

2. Exhausting duct for gases (plenum)

3. Main busbar compartment

4. Interrupting element compartment

5. Vacuum circuit breaker

6. Current transformers (CT)

7. Power cables

8. Earthing switch (grounding device)

9. Automatic shutters

10. Voltage transformers (VT)

11. Earthing (grounding) bar

Figure 16. An Example of Modern MV Metal-Enclosed Indoor

Air-Insulated Withdrawable Switchgear Unit Design Philosophy

Adopted by the Brazilian Petrochemical Sector

10

Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

Regarding the safety interlocks for circuit breaker cells and others

parts of the column, because ANSI and IEC follow very strict rules

to allow the operation of the system and interaction between

components, there was no significant change in customers'

requirements for such characteristics. Although an internal arc

fault would not be likely to occur in any switchgear and controlgear

assembly applied, erected, or used according to the standard's

guidelines and manufacturer's instructions, we could not disregard

such an event. So, similar to the ANSI directives for an internal arc

event (see ANSI C37.20.7), the IEC (and also ABNT) has its

own classification and guidelines to verify such classifications

(IAC—Internal Arc Classification).

The IAC classification includes accessibility, classified sides, arc fault

currents, and arc fault duration.

There are three types of accessibility:

• Type A: restricted to authorized personnel only

• Type B: unrestricted accessibility (general public)

• Type C: restricted by installation out of reach and above a general

public area

The classified sides are also identified by letters (this does not apply

to assemblies of accessibility type C):

• F: front side of the assembly

• L: lateral side of the assembly

• R: rear side of the assembly

In the petrochemical industry, as in any industrial electric substation,

due to the safety and operation requirements, the adopted

accessibility is "A" (restricted to authorized personnel only). So, the

authors have identified that the most common IAC classification

required for such sectors is AFLR (which would be similar to ANSI

Type 2 from ANSI C37.20.7 [23]).

Regarding the arc fault current and time values, the normal practice

is the adoption of the same value of the rated short-circuit current

with a time duration of 1 second.

As an example, we could have an IAC classification such as

"AFLR—40 kA—1 s", which is the capability to deal with an arc fault

current with a symmetrical value of 40 kA for 1 second at the front,

lateral, and rear sides of an assembly with accessibility restricted for

authorized personnel only.

Ergonomics

A common problem in electrical panels is the height of meters,

relays, and switches.

Because of the modular design, these devices are designed to be

at the top of the compartment, which causes difficulty when the

electrician needs to read a variable or check the reasons that a given

alarm was started, particularly in installations with microprocessor-

based relays [15].

Figure 17. End User Maximum Heights for Placing Instruments in

Electrical Panels, in Meters

The IEC and ANSI standards could include some requirements

regarding the height for placing the relays' displays. This would

make it easier for the professionals to take readings and to operate

more safely.

Brazilian end users include in their specifications some requirements

on ergonomics that need to be considered in a more effective way.

It is clear that it is necessary to discuss the benefits of this approach

related to the layout of electrical panels.

Figure 17 shows a Brazilian user specification [16] on heights for

placing instruments based on ergonomics.

11

Technical Data WP022001EN

IEEE November 2013

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

EATON www.eaton.com

Conclusions

The bottom line is that the application and safe use of MV metal-

enclosed switchgear assemblies demand a strong knowledge and

careful analysis in each specific case.

Years of experience with ANSI standardization and technology

built a strong reference for electrical professionals in the Brazilian

petrochemical sector. So, when the ABNT technical committees

responsible for the revision of electrical equipment standards followed

the government directive to embrace the IEC, many lessons learned

during years of using ANSI-based designs were brought to new

MV switchgear technical specifications. Brazil is experiencing an

interesting opportunity to prove the viability of increasing the efforts

done in the direction of a harmonization between ANSI and IEC,

especially as already seen in the area of high voltage circuit breakers.

The main Brazilian companies in the petrochemical segment

have been adopting some ANSI characteristics in the technical

specifications for MV switchgear that should also comply with IEC

in order to improve the entire performance of the equipment. This is

based on their long and positive experience with ANSI products.

The authors have seen the tendency in Brazil to enhance the

minimum requirements of IEC for such equipment with the ANSI

approach to improve safety and reliability.

At the end of this paper, we would also like to reinforce the

importance of educating new professionals and users about the

application and use of MV switchgear and controlgear assemblies.

Authors

Luiz Felipe Costa (M'2003, SM'2011) is a senior application engineer

for switchgear and control products with Eaton in Rio de Janeiro,

Brazil. He graduated with a degree in electrical engineering from

UFRJ Engineering School and was a postgraduate and major in the

protection of electrical systems at UNIFEI. He has over 27 years of

experience in project, testing, application, and commissioning of

switchgear and control of low and medium voltages.

Estellito Rangel Junior (M'2001, SM'2005) is a senior engineer with

Petrobras in its technical support department for offshore platforms.

He is member of the Brazilian Technical Standards Association

(ABNT) and has been involved with standards for hazardous locations

installations for over two decades. He is a Brazilian representative at

IEC technical committee 31, "equipment for explosive atmospheres,"

and has authored previous PCIC papers.

José Maria de Carvalho Filho is a professor and a member of GEQEE

(working group on electrical power quality studies) at Universidade

Federal de Itajubá (UNIFEI) in Itajubá, Brazil. He has over 30 years

of experience in industrial electrical power systems and power

quality analysis.

Rogério Barros is the service engineering coordinator at Eaton in

Rio de Janeiro, Brazil. He graduated from Universidade Veiga de

Almeida and has over 20 years of experience in project, budget

and quality control, manufacturing, assembly supervision, and the

implementation of switchgear and control of low and medium

voltages. He is currently responsible for technical sales activities

for Eaton's services in Brazil.

References

1. IEEE Standard for Metal-Clad Switchgear, IEEE Std

C37.20.2—1999.

2. IEC 62271-200. High-voltage switchgear and controlgear—

Part 20 switchgear and controlgear for voltages above 1 kV and

up to and including 52 kV. IEC; 2003.00: AC metal-enclosed

3. IEC 62271-1. High-voltage switchgear and controlgear—

Part 1: Common specifications. IEC; 2007.

4. IEC 62271-100. High-voltage switchgear and controlgear—

Part 100: AC circuit breakers. Edition 2.0. IEC; 2008.

5. IEC 62271-102. High-voltage switchgear and controlgear—

Part 102: AC disconnectors and earthing switches. IEC.

6. IEC 62271-106. High-voltage switchgear and controlgear—

Part 106: AC contactors, contactor-based controllers and motor

starters. Edition 1.0. IEC; 2011.

7. IEC 60529. Degrees of protection provided by enclosures

(IP Code). Edition 2.1. IEC; 2001.

8. IEC 60044-1. Instrument transformers—Part 1: Current

transformers. Edition 1.2. IEC; 2003.

9. IEC 60044-2. Instrument transformers—Part 2: Inductive voltage

transformers. Edition 1.2. IEC; 2003.

10. IEC 60282-1. High-voltage fuses—Part 1: Current limiting fuses.

Edition 5.0. IEC; 2002.

11. ABNT NBR IEC 62271-200. High-voltage switchgear and

controlgear. Part 200: AC metal enclosed switchgear and

controlgear for rated voltage above 1 kV and up to and including

36.2 kV. ABNT. 2007.

12. NBR 6979. Switchgear and controlgear assemblies in metallic

enclosure for rated voltage above 1 kV and up to and including

36.2 kV. ABNT; 1998.

13. IEC 60059—IEC standard current ratings. 2009.

14. IEC 60909-0—Short-circuit currents in three-phase AC systems—

Part 0: Calculation of currents. 2001.

15. Rangel Jr., Estellito and Bueno, Reginaldo, "How to get an

adequate electrical installation—Part II", in VIII Petrobras Electrical

Engineering Seminar, 2005, Conference Record.

16. ET-3000.00-5140-700 E—General criteria for electrical design.

Petrobras, 2007

17. ABNT NBR IEC 60694. Common specifications for high-voltage

switchgear and controlgear standard. ABNT, 2006.

18. IEC 60298—AC metal-enclosed switchgear and controlgear for

rated voltages above 1 kV and up to and including 52 kV. 1990

(third edition). It is not valid anymore. It was replaced in 2003 by [2].

19. IEEE Application Guide for AC High-Voltage Circuit Breakers

Rated on a Symmetrical Current Basis, IEEE Std C37.010—1999.

20. Chudnovsky, Bella. "Degradation of Power Contacts in Industrial

Atmosphere: Plating Alternative for Silver and Tin", IEEE IAS Pulp

and Paper Industry Conference.

21. Das, Jay C, and Mohla, Dallep C. "Harmonization of ANSI/IEEE

Standards for High-Voltage Circuit Breakers with IEC and Its

Impact on Application and Analysis", 2011 IEEE IAS Pulp and

Paper Industry Conference.

22. IEEE Standard for Metal-Enclosed Interrupter Switchgear,

IEEE Std C37.20.3—2001.

23. IEEE Guide for Testing Metal-Enclosed Switchgear Rated up to

38 kV for Internal Arcing Faults, IEEE Std C37.20.7—2007.

Link to IEEE original white paper.

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Publication No. WP022001EN / Z16800

June 2015

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of their respective owners.

Differences and similarities between

ANSI and IEC cultures for MV assemblies—

the Brazilian experience

Technical Data WP022001EN

IEEE November 2013

• J. C. Das
• Daleep C. Mohla

ANSI/IEEE standards for high voltage circuit breakers have undergone changes in the recent years to harmonize with IEC standards. An example of such harmonization is the peak ratings, TRV (transient recovery voltage) profiles, classifications, voltage range factor. The paper compares these changes with the existing prevalent standards and practices and their impact on the applications and analyses.

• B.H. Chudnovsky

Traditional silver and tin plating, exposed to specific corrosive gases, form heavy nonconductive scale of sulfides and oxides of the said metals, leading to overheating and multiple failures of circuit breaking equipment. The well-recognized anticorrosive properties of electroless Ni (EN) are widely used to protect various metals from corrosion, but it is rarely used for plating of electrical parts due to the relatively high electrical resistance of the plating layer which is of a non-crystalline nature. We found that EN plating with a predetermined content and thickness provides reliable and long lasting protection from corrosion in hot and humid atmosphere with high concentration of hydrogen sulfide, the specific gaseous environment of chemical plants, paper and steel mills, wastewater and sewage treatment plants, etc. Added to in-lab testing of corrosion and electrical properties of EN plating, we conducted a yearlong testing in the industrial environment of a wastewater treatment plant. This test showed that electroless Ni could effectively substitute traditional Ag and Sn plating and protect copper current carrying parts of circuit breaking equipment from damaging corrosion for a substantial period of time - up to one year without significant discoloration. We demonstrated through the series of life tests that re-plated equipment could be applied at the same ratings as originally designed by the manufacturer.

How to get an adequate electrical installation-Part II

• Rangel
• Estellito
• Reginaldo Bueno

Rangel Jr., Estellito and Bueno, Reginaldo, "How to get an adequate electrical installation-Part II", in VIII Petrobras Electrical Engineering Seminar, 2005, Conference Record.

High-voltage switchgear and controlgear. Part 200: AC metal enclosed switchgear and controlgear for rated voltage above 1 kV and up to and including 36.2 kV. ABNT

• Abnt Nbr Iec

ABNT NBR IEC 62271-200. High-voltage switchgear and controlgear. Part 200: AC metal enclosed switchgear and controlgear for rated voltage above 1 kV and up to and including 36.2 kV. ABNT. 2007.

Common specifications for high-voltage switchgear and controlgear standard

• Abnt

ABNT NBR IEC 60694. Common specifications for high-voltage switchgear and controlgear standard. ABNT, 2006.

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Source: https://www.researchgate.net/publication/273645622_Differences_and_Similarities_Between_ANSI_and_IEC_Cultures_for_MV_Assemblies-The_Brazilian_Experience