testing Of Circuit Breaker• Circuit breakers tests are Classified as follows: • Type test: These are performed solely for the purpose of proving the correctness of general design. Test conducted on a randomly selected breaker. Results are applied to all other identical construction. These tests can be performed by either by (a) Direct testing or (b) Indirect testing. • Routine test: These are performed for purpose of proving the correctness of assembly and material used. These are performed on each individual c.b. • The test procedures, methods of finding results, tests to be performed, etc. are specified by standard organizations. • On the recommendations of the International Electrotechnical Commission (IEC) vide publication No. 56-1 on the testing of a.c. circuit breakers. • Routine test include the following tests: A. Operational test. B. Measurement of resistance of the main circuits. C. One minute power frequency voltage dry withstand tests. Type tests • • Type tests are the test of one CB or a first few CBs of each type made to the same specifications. Type tests can be classified in following groups – Mechanical test – – – Thermal test Dielectric test Short circuit test ● ● ● ● Making capacity test Breaking capacity test Duty cycle tests Short time current tests . however lubrication is permitted as per manufacturer instructions.1) Mechanical test (Endurance test): • The breaker should be in a position to open and close satisfactory. • No adjustment or replacement of parts is permitted during the mechanical test. • In this test the CB is opened and closed several times (500). • After the test there should be no distortion or wear of parts. • Some operations (50) are by energizing the relay.c CB are conducted without current and voltage in the main circuit. • Mechanical test on a. . remaining are by closing the trip circuit by other means. 2) Thermal tests: • These are type tests to assign the normal current rating to the CB. • When a CB in closed condition carries normal current. . rise for rated current should not exceed 40º C for current less than 800 A normal current and 50º C for normal value of current 800 A and above. convection and radiation. the heat is generated in carrying parts due to I2Rt loss. • This heat is dissipated by conduction. • Alternating current of rated value and rated frequency is passed through a closed CB. • Readings of temperature of various conducting. insulating and structural parts are taken at an interval of one or halfan hour. the maxim temp rise of each part should be less than the permissible limit. • The temp. continuously till a steady temp is attained. • When the steady temp is reached. • To maintain the temp rise within specified limits.c current should be more than 100A and less than rated current of CB. • An additional requirement is the measurement of contact resistances between the isolating contacts and between the moving and fixed contacts. • The voltage drop across the breaker pole is measured for different values of d. using suitable low resistively material. • This points are main sources of excessive heat generation. • The d. conduction and radiation of heat.c. • This drop gives a measure of resistance of current carrying parts. currents. the resistance of breaker pole is measured at ambient air temp. . the resistance is of the order of few tens of micro-ohms. the I2Rt loss reduced by increasing conductor cross-section. and hence that of contacts. improving convection. 3) Dielectric test: • 1. 3. rated voltage. – – Across terminals with circuit breaker open. Between poles with circuit breaker closed. . Impulse tests. The test voltage with a frequency between 15-100 Hz is applied as follows: – Between poles and earth with circuit breaker open. These can be classified as Power frequency tests. For outdoor circuit dry and wet tests are conducted. Conducted on new circuit breaker . The test voltage varies with circuit breaker . These are conducted to confirm the rated insulation level of the circuit breaker. In this test impulse voltage of specified shape and magnitude is applied to the breaker. The voltage gradually increased and maintained at test value for 1 minute. Short circuit testing of C. Laboratory type testing station •. • These are conducted in short circuit testing stations.B • These tests are meant to prove the ratings of the circuit breaker. Short circuit testing is classified in further two types •. The field type testing station 2. • There are two types of short circuit testing stations 1. Direct testing •. Indirect testing . It is not possible to repeat the test again and again without disturbing networks.The field type testing station • In these tests are conducted by taking power directly from the system. The power available in the field testing station vary according to load connected on the network and layout of the network. It is difficult to set the system for the specified RRRV for breakers of high voltages. . hence not suitable for research and development work. but it suffers form the following drawback: That flexibility of the system available is limited. • It is most convincing method. • The test can be performed again and again in order to show the reproducibility of the results. . • The supply engineer can get satisfaction whether his breaker satisfies the requirements enunciated by specifications.Laboratory type testing station • It has special generators to supply power for the short circuit testing. • Such station is suitable for design engineer and supply engineer. • In this it is possible to vary the test condition as required. • The designer can study the behavior of arc rupture and make necessary improvements for higher voltages and higher breaking capacities. . • Further limitation and variation of current can be effected by means of tapped resistors and reactors. driven by induction motors. • The magnitude of the test voltage and the short circuit can be selected within wide limits by adjusting generators excitation and connection of the transformers. • This also serves control on power factor.Description of a simple testing station • In these testing stations the short-circuit power is supplied by specially designed short circuit generators. • Synchronized closing is controlled by means of a small pilot generator coupled to the generator shaft and can be very accurately set to occur at any instant within the voltage wave. . • With this the phase opposition at the commencement of short circuit can be selected.• The circuit is closed by specially designed make switch. • And short circuit current either fully symmetrical or with any degree of symmetry can be produced. designed for closing on very heavy currents. but never break currents. b. .b. • The recording equipment is located in a control room. • The breaker under test is enclosed in a test cell made of reinforced concrete having a provision of observation while test is in progress. is provided as a backup protection. under test to open the circuit. • By adding capacitor. • The control operations are carried out from the control room.• Master c. any desired high frequency can be obtained. in case of failure of c. connecting transformers to get desired test voltage etc. • The necessary preparation of C.• Direct testing involves subjecting a complete breaker or breaker pole to full power or stress during the test. . adjusting the magnitude of reactors. • The oscillographs are adjusted and calibrated. • The contacts on sequence switch are adjusted to get desired timings.B testing include connecting the equipment. . • The breaker under test is opened at desired moment • Making capacity test is necessary type test.B under test are closed first. the breaker under test is closed on a three phase short-circuit . • The master C.Bs are tested for their ability to make on to a Short-circuit. Short circuit is applied by closing the making switch.B and the make switch are closed first. Master circuitbreaker and C.• While testing breaking capacity. all C. 2) Breaking capacity: The braking capacity test should be performed with specified TRV of test Circuit 3) Peak making current: The peak making current made by the circuit breaker during the test should be expressed by maximum current in any pole.• Rules for type test 1) Breaking current: The short-circuit current broken by the CB should be measured at the instant of contact separation. 4) Condition of severity for making capacity and braking capacity tests are specified as under the following clauses: . 1) 2) 3) 4) 5) 6) 7) 8) 9) Conditions of breaker before test Conditions during the test Conditions of breaker after test Applied voltage before test Transient recovery voltage Short-circuit power factor Test frequency Earthing of test circuit Test duties . as all EHV CB are with several arc interrupter units per pole. .Indirect testing • The short-circuit power available in testing stations (which is of the order of 4000 MVA in lab type testing station) is no longer sufficient to test a complete breaker ( which is of rated breaking capacity of the order of 10. the capacity of the complete pole and breaker is determined. times that of the plant. This is called unit testing. • Synthetic testing is another popular method which permits testing of breaker of capacity 5.000 MVA at 245 KV) • Even single pole of a EHV CB cannot be tested by direct means. each unit can be separately tested. • From tests on one unit. the characteristics of current versus time are obtained for different voltages. Unit testing: which means testing one or more units separately. increase restriking voltages etc. Substitution test: These are conducted for oil CB. Capacitance tests: the capacitor which is charged by a voltage source is discharged through the breaker. Synthetic testing: In which the current source providing short circuit current and voltage source supplying restriking and recovery voltage are different 3. 8.The important indirect Methods include the following: 1. 2. . the performance beyond the tested value is determined by approximation 7. Compensation tests: which are conducted on oil CB in critical range of low current by suitable compensation such as increased frequency. an oscillatory circuit provides restriking voltage. SYNTHETIC TESTING . the voltage source provides restriking voltage plus recovery voltage. Other L. the switch S1 is closed to supply short-circuit current IG.C etc are used to get desired test conditions. the voltage will have transient because of L and C of the circuit . At near final current zero switch S2 ( which is usually a spark gap) is closed and V3 to applied to the breaker at an appropriate moment.• 1) 2) •) •) •) The synthetic test employs two sources namely Current source (of relatively low voltage) Voltage source (of relatively low current) The current source provides short-circuit current.r. V • The short-circuit generator has to supply currents at a relatively less voltage ( as compared to direct testing) • Both test current and test voltage can be independently varied. . so test become flexible • This is a simple method and can be applied to unit testing • With this method a breaker of capacity of five time that of the capacity of the test plan can be tested.R.R.• Advantages of this method • The breaker can be tested for desired TRV and R. Types of Synthetic Test circuits: There are two types of synthetic circuit Parallel current injection method . • In parallel current injection method. the voltage circuit (2) is effectively connected in parallel with current circuit (1) and the test breaker before the main current IG in test breaker current is properly simulated. . Series current injection Method . t4 etc .t3. as a result IH and IG are in opposition to breaker circuit Several factors influence the stress during the test like 1) high current mode 2) Instant of applying voltage 3) Frequencies of TRV etc 4) High voltage mode 5) t1.t2. the voltage circuit (2) is connected to current circuit in series before main current zero.• In series current injection method.