Issued by : Switchgear Contracts Division LARSEN & TOUBRO LIMITED Powai Works, Mumbai October December 1996

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Issued by : Switchgear Contracts Division LARSEN & TOUBRO LIMITED Powai Works, Mumbai 400 072.

1 Issued by : Switchgear Contracts Division LARSEN & TOUBRO LIMITED Powai Works, Mumbai October December 1996 Prospect/ Retrospect IS/IEC Specification In the previous three issues of L&T Current Trends, we have published an article on IS/IEC specification for Low Voltage Switchgear and Controlgear (IS 13947) in three parts. Our readers have written to us to give a condensed summary of these three parts. In this issue, we are publishing the summary alongwith important tables which were included in main article. Though our efforts are to make this summary as exhaustive as possible, so that it can be preserved by our readers as a handy reference, if any clarification is required, we suggest that our readers refer to the original Indian Standards. FEATURE Introduction to IS : A new Indian Standard on Switchgear and Controlgear Products - Summary - H.T. Mistry, Senior Executive-Design, Switchgear Design and Product Development In a major revision, International Electrotechnical Commission (IEC) introduced a new specification, IEC 947, on low voltage switchgear and controlgear in Bureau of Indian Standards also decided to adopt the text of IEC 947 and consequently, in1993, introduced a new dual number specification IS 13947/ IEC pub 947 on switchgear and controlgear products. National Annex has been added to IEC text in IS to cover typical requirements e.g. use of aluminium conductors, ambient conditions, preferred voltages. etc. This specification is divided into two documents. as general have been consolidated in this first part. 2) Product standard Specific testing and performance requirements of the products are covered by relevant product standards. These are : Part 2 : Circuit breakers Part 3 : Switches, disconnectors, switch disconnectors and fuse combination units Part 4 : Contactors and motor starters (section 1 : Electromechancal contactors and starters) 1) General rules (Part 1) : All those parts of various prooduct standards which can be considered Part 5 : Control circuit devices and switching elements Part 6 : Multiple function devices

2 Part 7 : Ancillary equipments PART 1 : GENERAL RULES : This standard states those general rules and requirements which are common to low voltage switchgear products e.g. definitions; characteristics; normal service, mounting and transport conditions; information to be supplied with the equipment; constructional and performance requirements and verification of these requirements. Following are the major revisions introduced in part 1 : I) DEFINITIONS : Disconnector: Definition of disconnector has been enlarged. A disconnector has now been defined as a mechanical device which in the open position complies with the requirements of isolating function. As per the new definition, a disconnector needs to meet performance requirements in addition to minimum isolating distance. II) RATINGS AND LIMITING VALUES : i) Conventional thermal currents Following two new limiting currents have been introduced to define thermal characteristics of the product. a) Conventional free air thermal current (Ith) b) Conventional enclosed thermal current (Ithe) These currents are defined as the maximum values of currents to be used for temperature rise tests on unenclosed equipment (Ith) or on equipment in smallest enclosure specified by the manufacturer (Ithe). These currents are not the ratings and need not be marked on the equipment. ii) Rated impulse withstand voltage (Uimp) : Overvoltages originate from causes like load fluctuations, switching operations, resonances, faults and lightening discharges on low voltage (LV) systems. These overvoltages affect common LV installations and equipment. In view of this, in order to evaluate adequacy of design of low voltage switchgear products to withstand overvoltages, concept of rated impulse withstand voltage has been introduced. Preferred values of rated impulse withstand voltage are specified in new IS. Theses are reproduced in table 1. Overvoltage category for the equipment is decided by its location in the installation. (Origin of installation, distribution, load etc.) Preferred value of impulse withstand voltage reduces as the equipment is located further away from the source of energy. I) NORMAL SERVICE CONDITIONS : Pollution degrees : In order to define environmental conditions more precisely and to evaluate clearance and creepage distances following four pollution degrees are established. Pollution degree 1 : No pollution or only dry, non-conductive pollution occurs. Pollution degree 2 : Normally non-conductive pollution occurs. Occasionally, however, a temporary conductivity caused by condensation may be expected. Pollution degree 3 : Conductive pollution occurs or dry, non-conductive pollution occurs which becomes conductive due to condensation. Pollution degree 4 : The pollution generates persistent conductivity caused, for instance, by conductive dust or rain of snow. Unless otherwise specified equipment or industrial application is generally suitable for use in pollution degree 3 environment. II) CONSTRUCTIONAL REQUIREMENTS : a) Materials : The suitability of insulating material is verified with respect to its resistance to abnormal heat and fire through elaborate tests. These tests are either conducted on the equipment (glow wire test) or on specimen of the material (hot wire ignition and arc ignition tests). b) Terminals : Constructional requirements e.g. strength, size etc. for terminals suitable for unprepared copper conductors are evaluated through following tests. i) Tests for verification of mechanical strength ii) Flexion test (test for damage to conductors and their accidental loosening) iii) Pull out test iv) Test for insertability of conductors c) Clearance and creepage distances : Clearance : Minimum clearance values have been specified in new IS on the basis of rated impulse withstand voltage and pollution degree. Clearance is verified through a type a test for verification of dielectric properties. To account for deterioration of properties of insulating materials minimum creepage distance are specified based on following factors

3 - Rated insulation voltage - Environmental conditions or pollution degree - Insulating materials used b) Short circuit ratings : Following two new short circuit ratings have been introduced. i) Rated ultimate short circuit breaking capacity (Icu) : Minimum number of operations for breakers for ratings up to 100A and above 1250A have been revised as shown in table VI. c) Number of units to be tested : Insulating materials can be roughly characterized according to the damage they suffer due to flow and interruption of leakage current on contaminated surfaces. Though no direct relationship exists, it has been found by tests and experience that insulating materials with higher comparative tracking index (CTI) have relatively better performance. Hence for the purpose of specifying minimum creepage distance, insulating materials have been classified into four material groups in terms of CTI, as given in table II. Minimum creepage distances for low voltage switchgear products are given in table III. PART 2 : CIRCUIT BREAKERS This standard replaces IS 2516 (Parts 1&2/Sec. 1)-1985 I) CHARACTERISTICS : a) Utilization category : 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). 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. This rating is similar to P1 category rating defined in IS ii) Service short circuit breaking capacity (Ics) : Service short circuit breaking capacity is also assigned by the manufacturer and can be expressed as percentage of ultimate short circuit breaking capacity (Icu). The ratio shall be selected from standard ratios indicated in table IV. This rating is similar to P2 category rating 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 V. b) Operational performance capability : This test, a part of test sequence 1, is to verify capability of breakers to perform minimum number of mechanical (without current) and electrical (with current) operations. Number of units to be tested is arrived at based on whether - the product is assigned more than one operational voltage - terminals for line and load connections are identified d) Conductors for short circuit test : For circuit breakers of ratings upto 630A, 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." PART 3 : SWITCHES, DISCONNECTORS, SWITCH DISCONNECTORS AND FUSE COMBINATION UNITS This part replaces both parts of IS Following changes have been incorporated in the new IS. I) CHARACTERISTICS : a) Rated short time withstand current (Icw) : 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

4 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. Utilization categories with suffix B are appropriate for devices which, due to design or application, are only intended for infrequent operations. Category AC 23A includes occasional switching of individual motors. II) PERFORMANCE REQUIREMENTS : Performance requirements are verified through type tests. All relevant type tests are grouped into four test sequences. These are given in table VII. Performance requirements have, in general, become more onerous. Expected minimum electrical and mechanical life corresponding to rating have been indicated. Expected life for category A is higher than category B. PART 4 : CONTACTORS AND MOTOR STARTERS : SECTION 1 : ELECTROMECHANICAL CONTACTORS AND STARTERS: So far, requirements of contactors and motor starters were covered by separate standards, namely IS 2959 and four parts of IS 8544 respectively. These are now covered by part 4/Section 1 of IS There are significant changes in performance requirements. Attempt has also been made, wherever possible, to align with North American practices. I) Utilization categories : In the new IS scope has been widened to include various applications of contactors. These are listed in Table VII. Presently, utilization categories are characterised by i) rated making and breaking capacities of the contactors and ii) electrical life. In the new IS, one more criterion, conventional operational performance, has been introduced. This requirement does not evaluate expectancy of life but verifies capability of the contactor to make and break, for specified number of times, normal and marginal overload currents. II) Terminal markings : The terminals for main circuits are required to be marked by a single digit number (IEC 445) and aplhanumeric system (North American practice). III) Trip classes for overload relays : In the new IS, selection of relay has been facilitated by introduction of trip classes. Relays are classified into four trip classes based on tripping time at 7.2 times the setting of the relay. In other words, trip classes indicate maximum motor starting time permitted by the relay.. Trip classes are indicated in Table IX. Definition of trip classes 10, 20 and 30 is in line with North American standards. IV) Tests : a) Test sequences : All type tests are segregated in five test sequences. b) Performance under short circuit condition : In new IS, this test has been significantly revised as follows : 1) Performance is verified through three tests : a) Verification to short circuit performance at "r" current, "r" current is decided corresponding to maximum AC3 rating as indicated in table X. b) Verification of short circuit performance at "q" current declared by the manufacturer c) Verification of co-ordination at "p" current. (a) and (b) are now mandatory tests while (c) is a special test. (2) Only two types - type 1 and 2 - of co-ordinations are specified in new IS instead of three types - type A, B and C as in IS Type of co-ordination, is defined based on the extent of damage during short circuit test. For type 1 co-ordination, damage to the contactor/starter is permitted. However, there should be no danger to the operator or damage to the installation. These conditions are similar to those for type A co-ordination. No damage is permitted for type 2 coordination. However, light contact welding which can easily be opened (with a screw driver) is acceptable. This is analogous to type C coordination. Type B co-ordination defined in IS 8544 has been excluded. For type B co-ordination, no damage was permitted except alteration of overload relay characteristics. For further information, please contact Larsen & Toubro Limited, Packing Division, Powai Works, Saki-Vihar Road, Mumbai Edited, printed and published by Cerena de Souza for Larsen & Toubro Limited. Published from L&T House, Narottam Morarjee Marg, Balard Estate, Mumbai and printed at Uma Offset, 359, A to Z Indl. Estate, G. Kadam Marg, Lower Parel, Mumbai Associate Editor: Luis S. R. Vas.

5 Table I PREFERRED VALUES OF IMPULSE WITHSTAND VOLTAGE MAXIMUM VALUE OF TATED OPERATIONAL VOLTAGE TO EARTH V IV ORIGIN OF INSTALLATION PREFERRED VALUES OF IMPULSE WITHSTAND VOLTAGE in kv (1.2 / 50 µs) OVER VOLTAGE CATEGORY III DISTRIBUTION CIRCUIT II LOAD I SPECIALLY PROTECTED TABLE - III MINIMUM CREEPAGE DISTANCES RATED INSULATION VOLTAGE, V POLLUTION DEGREE 2 CREEPAGE DISTANCES, in mm POLLUTION DEGREE 3 POLLUTION DEGREE 4 MATERIAL GROUP I II IIIA IIIB MATERIAL GROUP I II IIIA IIIB MATERIAL GROUP I II IIIA IIIB TABLE II MATERIAL GROUPS MATERIAL GROUP I 600 <= CTI MATERIAL GROUP II 400 <= CTI < 600 MATERIAL GROUP IIIa 175 <= CTI < 400 MATERIAL GROUP IIIb 100 <= CTI < q 32 - TABLE V : CIRCUIT BREAKERS - TEST SEQUENCES TABLE IV Standard ratios between Ics and Icu Utilization Utilization Category A Category B Ics (as % of Icu) Ics (as % of Icu) TEST SEQUENCE APPLICABLE TO TESTS I General Performance Characteristics II Rated service s.c. breaking capacity (Ics) III Rated ultimate s.c. breaking capacity (Icu) IV Rated short time withstand current (Icw) Combined test sequence. All circuit breakers All circuit breakers All circuit breakers Circuit breaker of utilization category B 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.Tripping limits and characteristics 2.Dielectric properties 3.Operational performance capability 4.Overload performance 5.Verification of dielectric withstand 6.Verification of temperature rise 7.Verification of overload releases 1.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 ultimate s.c. breaking capacity 3.Verification of dielectric withstand 4.Verification of overload releases 1.Verification of overload releases 2.Rated ultimate s.c. breaking capacity 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 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

6 RATED A TABLE VI : CIRCUIT BREAKERS COMPARISION OF MINIMUM OPERATING CYCLES WITHOUT IS IS 2516 MINIMUM OP. CYCLES MINIMUM OP. CYCLES WITH TOTAL WITHOUT WITH TOTAL In < = 100 A < In < = < In < = < In Subject to agreement TABLE VIII Utilization categories for contactors/starters IS (Part 4/Sec. 1) Utilization category AC-1 AC-2 AC-3 AC-4 AC-5a AC-5b AC-6a AC-6b Typical applications Non inductive or slightly inductive loads resistance furnaces Slip-ring motors: starting, switching off Squirrel cage motors: starting, switching off while running Squirrel cage motors: starting, plugging, inching Switching of electric discharge lamp controls Switching of incandescent lamps Switching of transformers Switching of capacitor banks TABLE VII : SWITCHES, DISCONNECTRS, FUSE COMBINATION UNITS TEST SEQUENCES TEST SEQUENCE I General performance characteristics II Operational performance capacity III Short circuit performance capability IV Conditional short circuit current TEST (1) Temperature rise (2) Dielectric properties (3) Making and breaking capacities (4) Dielectric verification (5) Leakage current (6) Temperature rise verification (7) Strength of actuator mechanism (1) Operational performance (2) Dielectric verification (3) Leakage current (4) Temperature rise verification (1) Short time withstand current (2) Short circuit making capacity (3) Dielectric verification (4) Leakage current (5) Temperature rise verification (1) Fuse protected s.c. withstand (2) Fuse protected s.c. making (3) Dielectric verification (4) Leakage current (5) Temperature rise verification AC-8a AC-8b DC-1 DC-3 DC-5 DC-6 Hermatic refrigerent compressor motor control with manual resetting of overload releases Hermatic refrigerent compressor motor control with automatic resetting of overload releases Non-Inductive or slightly inductive loads resistance furnace Shunt motors: starting plugging, inching, dynamic braking of d. c. motors. Series motors: starting, plugging, inching dynamic braking of d. c. motors. Switching of incandescent lamps Table X Value of r current IS (Part 4/sec. 1) Table IX Trip classes for overload relays IS (Part 4/sec. 1) Trip Class Tripping time, Sec. * 10A < Tp <= 10 4 < Tp <= 10 6 < Tp <= 20 9 < Tp <= 30 * At 7.2 times relay setting starting from cold Rated Operational Current Ie (AC3), A 0 < le <= < le <= < le <= < le <= < le <= < le <= < le <= < le r Current ka Subject to agreement

AF series contactors (9 2650)

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