Overcurren Relay MCGG 82, 52 dan 22

MCGG 22 Single phase overcurrent with instantaneous element. MCGG 42 Two phase overcurrent with instantaneous elements. MCGG 52 Two phase overcurrent plus earth fault with instantaneous elements. MCGG 53 Two phase overcurrent ( with polyphase measurement) plus earth fault with instantaneous elements. MCGG 62 Three phase overcurrent with instantaneous elements. MCGG 63 Three phase overcurrent ( with polyphase measurement) , with instantaneous element. MCGG 82 Three phase overcurrent plus earth fault with instantaneous elements. Associated publications: Midos System R6001 Directional Relay R6003 The relay can be used in applications where time graded overcurrent and earth fault protection is required. The relay can be used to provide selective protection for overhead and underground distribution feeders. Other applications include back-up protection for transformers, generators and HV feeder circuits and the protection of neutral earthing resistors. With all the current/ time characteristics available on one relay, a standard relay can be ordered before detailed co-ordination studies are carried out – a distinct advantage for complex systems. Also, changes in system configuration can be readily accommodated. An instantaneous element with low transient overreach is incorporated within each phase or earth fault measuring board. This can be easily disabled in applications where it is not required. For applications where the instantaneous earth fault element is required to have a sensitive setting whilst remaining stable on heavy through faults the use of a stabilising resistor is recommended. The current transformers for this application must satisfy the criteria detailed under ‘ Current transformer requirements’ in Technical Data. The total impedance of the relay and the series stabilising resistor is usually low enough to prevent the current transformers developing voltages over 2kV during maximum internal faults, but in some applications a non-linear resistor is required to limit this voltage. Non-standard resistance values and non-linear voltage limiting devices are available. Description This range of MCGG relays is designed so that versions are available with separate measuring boards for each phase or earth fault input; alternatively, phase inputs may be combined on to one board for polyphase measurement ( see table) . These boards, together with the other circuits of the relay, are contained in Switch position Operating ( 0) ( 1) characteristic l l Trip test l l l Standard inverse sec SI l l l Very inverse sec VI l l l Extremely inverse sec EI l l l Long time earth fault sec LT l l l Definite time 2 seconds D2 l l l Definite time 4 seconds D4 l l l Definite time 8 seconds D8 l Table1: Operating time characteristics with corresponding switch positions. t = 0.14 ( I0.02 – 1) t = 13.5 ( I – 1) t = 80 ( I2 – 1) t = 120 ( I – 1) a single plug-in module which is supplied in a size 4, 6 or 8 Midos case. The case incorporates one or two terminal blocks for external connections. Removal of the module automatically short circuits the current transformer connections by means of safety contacts within the case terminal block. For added security, when the module is removed, the ct circuits are short circuited before the connections to the output contacts and the dc supply are broken. The relay uses solid state techniques, each measuring board utilising a microcomputer as a basic circuit element. The current measurement, whether performed on a single phase or polyphase input, is performed via an analogue-to-digital converter. Application diagrams are provided in Figures 2 to 8 ( inclusive) showing typical wiring configurations. Each measuring board has a built-in ‘ power off’ memory feature for the time delayed and instantaneous led indicators. Power to each measuring board may be tested whilst the relay is in service. without affecting the current measurement. A test mode is also available to carry out a trip test on the output relays. During this test, current measurement is inhibited. When required, directional control can be exercised over the relay by connecting an output contact from direction relay type METI to the terminals provided. Separate output contacts, capable of circuit breaker tripping, are provided for time delayed phase faults, instantaneous phase faults, time delayed earth fault and instantaneous earth fault operations. Relay settings Separate setting switches for each measuring board are provided on the relay frontplate. These are used to select the required time/ current characteristic, current and time multiplier settings. Selection of time characteristics The current/ time characteristic selection is carried out by means of three switches ( identified by symbol on the nameplate) . Table 1 gives the basic operating characteristic and the settings of the switches.