Issued by : Switchgear Contracts Division LARSEN & TOUBRO LIMITED Powai Works, Mumbai 400 072
April - June 1996
Prospect / Retrospect
Creating
Benchmarks
A new product or feature is
conceptualised to meet demands
which cannot be taken care of by
existing product or feature. When this
new product is manufactured and put
into operation, it caters of some of
the expectations, but by that time,
technological advances change
surrounding parameters. So it
becomes necessary to define the
parameters under which the product
is expected to deliver its desired
performance. And also it is essential
to define what is meant by desired
performance.
Standards are defined to set and
state these parameters. Standards
paraphrase conditions in which the
product is expected to perform and
they also define what should be the
desired performance. In a
competitive market, standards create
benchmarks which all similar
functioning products are expected to
meet or surpass. Thus, in a way,
L&T PRODUCTS
L&T's Air Circuit Breakers type
C-Power have been successfully
tested for various requirements of IS
13947 (Part 2)-1993 and IEC 9472(1989) at Central Power Research
Institute (CPRI), Electrical Research
& Development Association (ERDA)
and Association of Short Circuit
Testing Authorities, U.K. (ASTA).
standards set reference line; they
form the rules for the game.
When technology all around is
progressing, the standards cannot
remain rigid. They have to reflect
real life situations. They should also
incorporate customer's higher
expectations. The benchmarks set
once need to be reviewed and
upgraded whenever essential.
A proper co-ordination between
advancement in technology and
realistic stipulated conditions for
performance can result in an efficient
product with optimum cost,
benefiting both the customer and the
supplier.
In the last issue of L&T Current
Trends, we highlighted major
revision in LV Switchgear standards
laid down in Part I of IS 13947.
This article will be concluded in the
next issue.
C-Power ACB
L&T switches, type FF and FFO and
Fuse combination units, type FN63,
FN125 and FN200 comply with IS
13947(Part 3)-1993.
FEATURE
Introduction to IS 13947 :
A new Indian Standard on
Switchgear and Controlgear Products-II
- H. T. Mistry, Senior Executive-Design, Switchgear Design and Product Development
In the previous issue, we discussed
revisions in general requirements for
low voltage switchgear and
controlgear products covered by Part
1 of IS 13947. In this issue, we shall
discuss Part 2 and Part 3, product
standards pertaining to low voltage
circuit breakers, switches and fuse
combination units respectively.
PART 2 : CIRCUIT BREAKERS :
This standard replaces IS 2516
(Parts 1&2 / Sec. 1)-- 1985.
The objective of this standard is to
state performance and construction
requirements for circuit breakers and
to lay down verifying tests. There are
significant revisions in these
requirements. These are explained in
following pages.
(I) CHARACTERISTICS :
(a) Utilization category :
So far utilization categories were
defined only for contactors and
switches. In the new IS utilization
categories have been specified for
circuit breakers also. These have
been defined with reference to
selectivity i.e. whether a circuit
breaker is intended for selectivity by
means of an intentional time delay
under short circuit conditions.
Circuit breakers not specifically
intended for selectivity can be
assigned utilization category A e.g.
moulded case circuit breakers. These
breakers need not have short time
withstand rating (Icw).
Circuit breakers specifically meant for
selectivity are assigned utilization
category B. Air circuit breakers with
intentional time delay for tripping in
short circuit condition can be
assigned utilization category B.
These breakers will also be assigned
short time withstand rating (Icw).
(b) Short circuit ratings :
Following two new short circuit
ratings have been introduced.
(i) Rated ultimate short circuit
breaking capacity (Icu):
Ultimate short circuit breaking
capacity is assigned by the
manufacturer.
As the term indicates, continued
service from the breaker is not
expected after the breaker has
cleared a short circuit fault of such
magnitude. Hence, the prescribed
test conditions do not include
verification of capability of breaker to
carry its rated current after short
circuit test.
This rating is similar to P1 category
rating defined in IS 2516.
Prescribed test conditions include
verification of capability of the
breaker to carry its rated current after
short circuit test implying expectation
of continued service (carrying rated
current) till the breaker is replaced.
This rating is similar to rating
corresponding to P2 category
specified in the earlier standard.
(II) PERFORMANCE
REQUIREMENTS :
(a) Test sequences :
In order to evaluate performance of a
product comprehensively, relevant
type tests are grouped into test
sequences. All tests in a given
sequence are carried out on the
same unit in prescribed order. Such
sequential testing represents actual
service conditions more closely.
Details of test sequences applicable
to circuit breakers are given in table 1.
(b) Operational performance
capability :
(ii) Service short circuit breaking
capacity (Ics) :
This test, a part of test sequence 1, is
to verify capability of breakers to
Service short circuit breaking
perform minimum number of
capacity is also assigned by the
mechanical (without current) and
manufacturer and can be expressed
electrical (with current) operations.
as percentage of ultimate short circuit
Minimum number of operations for
breaking capacity (Icu). The ratio
breakers for ratings up to 100 A and
shall be selected from standard ratios
above 1250 A have been revised as
indicated below.
shown in table 2.
Standard ratios between Ics and Icu
Utilization
Utilization
Category A
Category B
Ics (as % of Icu)
Ics (as % of Icu)
25
50
75
100
50
75
100
(c) Number of units to be used :
Number of units to be tested for each
test sequence is now laid down. This
ensures complete evaluation of the
product performance.
Number of units to be tested is
arrived at based on whether
TABLE 1 : CIRCUIT BREAKERS -- TEST SEQUENCES
TEST
SEQUENCE
I
General performa
characteristics
APPLICABLE TO
All circuit breakers
1.
2.
3.
Tripping limits and characteristics
Dielectric properties
Operational performance
capability
4. Overload performance
5. Verification of dielectric withstand
6. Verification of temperature rise
7. Verification of overload releases
All circuit breakers
1.
III
Rated ultimate s.c.
breaking capacity
(Icu)
All circuit breakers
1.Verification of overload releases
2.Rated ultimate s.c. breaking capacity
3.Verification of dielectric withstand
4.Verification of overload releases
IV
Rated short time
withstand current
(Icw)
Circuit breaker of
utilization category B
Rated service s.c. breaking
capacity
2. Verification of dielectric withstand
3. Verification of temperature rise
4. Verification of overload releases
1.Verification of overload releases
2.Rated short time withstand current
3.Verification of temperature rise
4.S.c. breaking capacity at maximum
short time withstand current
5.Verification of dielectric withstand
6.Verification of overload releases
Circuit breakers of
utilization category B
i) when Icw=Ics
(Replaces Seq II & IV)
ii) when Icw=Ics=Icu
(Replaces Seq II,III&IV)
1.Verification of overload releases
2.Rated short time withstand current
3.Rated service s.c. breaking capacity
4.Verification of dielectric withstand
5.Verification of temperature rise
6.Verification of overload releases
TABLE 2 : CIRCUIT BREAKERS
COMPARISION OF MINIMUM OPERATING CYCLES
RATED CURRENT
the product is assigned more
than one operational voltage
-
terminals for line and load
connections are identified
TESTS
II
Rated service s.c.
breaking capacity
(Ics)
Combined test
sequence
-
IS 13947-2
MINIMUM OP.CYCLES
IS 2516
MINIMUM OP.CYCLES
WITHOUT
CURRENT
WITH
CURRENT
TOTAL
WITHOUT
CURRENT
WITH
CURRENT
TOTAL
In < = 100 A
8500
1500
10000
4000
4000
8000
630 < In < = 1250
2500
500
3000
2500
500
3000
1250 < In < = 250
2500
500
3000
900
100
1000
2500 < = In
1500
500
2000
This is elaborated in table 3.
(d) Conductors for short
circuit test :
For circuit breakers of ratings up to
630 A, conductors to be used for
terminal connections in short circuit
tests (Ics and Icu) have now been
specified as given below.
"A cable of 75 cm in length having a
cross section corresponding to the
conventional thermal current shall be
included as follows :
- 50 cm on supply side
- 25 cm on load side
This requirement portrays actual
application more realistically.
PART 3 : SWITCHES,
DISCONNECTORS, SWITCH
DISCONNECTORS AND FUSE
COMBINATION UNITS
This part pertains to low voltage
switches, disconnectors, switch
disconnectors and fuse combination
units and replaces both parts of IS
4064 - 1978.
Following changes have been
incorporated in the new IS.
(I) CHARACTERISTICS :
Subject to agreement
(a) Rated short time withstand
current (Icw) :
TABLE 3 : CIRCUIT BREAKERS - NUMBER OF UNITS FOR TEST SEQUENCES
TEST SEQUENCE
I
II (Ics)
AND
COMBINED
III (Icu)
IV (Icw)
NO. OF MARKED
WHETHER TERMINALS
OPERATIONAL VOLTAGE
MARKED LINE / LOAD
1
2
MULTIPLE
YES
NO
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
AS PER TEST SEQUENCE III
Example : For sequence II and combined test sequence, if the breaker is a
assigned one operational voltage and line/load terminals are not
identified than three breakers need to be tested.
NO. OF SAMPLES
FOR TEST
1
2
3
3
4
2
3
3
4
This characteristics has been revised.
As per IS 4064, minimum short time
withstand current was 20 times the
maximum rated operational current
for a duration of 1 second. This has
been changed to 12 times the
maximum rated operational current.
(b) Utilization category :
Designation of utilization category
has been changed. In the new IS,
The designation is completed by
suffix A or B according to whether the
intended applications require
frequent or infrequent operations.
Table 5 : SWITCHES, DISCONNECTORS, FUSE COMBINATION UNITS
COMPARISION TEST PARAMETERS FOR AC 23A CATEGORY
IS 13947-3
RATING, A
Utilization categories with suffix B are
appropriate for devices which, due to
design or application, are only
intended for infrequent operations.
I/ie
10
10
Ie <= 17
17 < Ie <= 100*
100 < Ie
MAKE
U/Ue
p.f.
Ir/Ie
1.05
1.05
0.45
0.35
8
8
IS 4064
MAKE/BREAK
Ur/Ue
1.05
1.05
p.f.
I/Ie
MAKE
U/Ue
0.45
0.35
10
10
8
1.1
1.1
1.1
p.f.
0.65
0.35
0.35
I/Ie
8
8
6
BREAK
U/Ue
1.1
1.1
1.1
p.f.
0.65
0.35
0.35
* FOR IS 13947-3, THIS RANGE IS Ie < = 100 A
Typical applications covered by
various utilization categories,
however, have remained
unchanged.
(II) PERFORMANCE
applicable to equipment normally
used to start, accelerate and / or stop
REQUIREMENTS :
individual
motors
(e.g.
AC
2,
AC
3/4)
Category AC 23A includes
are covered in appendix A. These
(a) Test sequences :
occasional switching of individual
were
hitherto
covered
by
part
2
of
motors. Utilization categories
All relevant type tests are grouped
IS 4064.
into four test sequences. These are
given in table 4.
TABLE 4 : SWITCHES, DISCONNECTORS, FUSE COMBINATION UNITS
TEST SEQUENCES
TEST SEQUENCE
TEST
(b) Making and breaking capacity :
I
General performance
characteristics
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Temperature rise
Dielectric properties
Making and breaking capacities
Dielectric verification
Leakage current
Temperature rise verification
Strength of actuator mechanism
Test parameters for this test have
been significantly modified. These
are summarized below :
II
Operational performance
capability
(1)
(2)
(3)
(4)
Operational performance
Dielectric verification
Leakage current
Temperature rise verification
III
Short circuit performance
capability
(1)
(2)
(3)
(4)
(5)
Short time withstand current
Short circuit making capacity
Dielectric verification
Leakage current
Temperature rise verification
IV
Conditional short circuit current
(1)
(2)
(3)
(4)
(5)
Fuse protected s.c. withstand
Fuse protected s.c. making
Dielectric verification
Leakage current
Temperature rise verification
(i)
(ii) Test voltage is 1.05 times rated
operational voltage instead of
1.1 times.
TABLE 6 : SWITCHES, DISCONNECTORS, FUSE COMBINATION
UNITS - COMPARISON OF MINIMUM OPERATIONS
RATING,A
0 < Le < = 63
63 < Ie < = 100
100 < Ie < = 250
250 < Ie < = 315
315 < Ie < = 630
630 < Ie < = 800
800 < Ie < = 2500
2500 < Ie
IS 4064
MINIMUM OP.CYCLES
@ IS 13947-3
MINIMUM OP.CYCLES
$ WITHOUT
CURRENT
WITH #
CURRENT
WITHOUT
CURRENT
WITH
CURRENT
10000
3000
3000
1000
1000
1000
300
300
500
150
150
50
50
50
15
15
8500
8500
7000
7000
4000
2500
2500
1500
1500
1500
1000
1000
1000
500
500
500
# Unless specified, 1/20 th of mechanical (without current)
operating cycles specified by the manufacturer.
$ Unless otherwise stated by the manufacturer
@ For utilization categories AC2*A. Requirements are lower
for utilization categories AC2*B.
This test can be carried out in
two parts viz. test for making
capacity followed by test for
breaking capacity. However,
unlike IS 4064, make operations
are followed by make-break
operations instead of only break
operations.
(iii) Test currents for AC 23A have
been revised upwards as
indicated in table 5.
However, number of operations for
ratings higher than 100A has been
reduced from 5 to 3.
(c) Operational performance :
These tests are a part of test
sequence 2 and are intended
to verify capability of the
equipment to perform specified
number of operations, with and
without current flowing in the
main circuit.
Minimum number of operations
expected have been revised as
shown in table 6.
For further information, please contact Switchgear Contracts Division, Larsen & Toubro Limited, Saki-Vihar Road, mumbai 400 072.
Edited, printed and published by Cerena de Souza for Larsen & Toubro Limited. Published from L&T House, Ballard Estate, Mumbai 400 001,
and printed at Uma Offset, A to Z Indl. Estate, G. Kadam Marg, Lower Parel, Mumbai 400 013. Associate Editor: Luis S. R. Vas.