GE DS200TCDAG2B Vector signal transceiver

Selectivity between medium and low voltage With protection selectivity it is meant the capability of the trip unit (or, more generally, of the protection) to distinguish the type of fault and its location and to trip only in case of faults occurring in the area for which the protection is provided. To carry out a selectivity study between MV and LV circuit-breakers, it is necessary to insert in a logarithmic diagram (referred to a defined voltage) the main parameters, that is: 1. for the transformer: • magnetizing curve; • rated current; • short-circuit current of the busbars on the LV side; • short-time current of the transformer. 2. for the upstream network: • time-current characteristic of the protection device owned by the distri bution Authority

Once these information have been traced out

the protection curve on the LV side can be drawn, taking into account the following limitations: • the transformer must be protected against overload; • the protection must be selective in comparison with other LV protections. Once the curve of the LV protection is known, the limits of the MV protection can be defined keeping into account that: • it must protect the transformer against overload (if this protection is not already guaranteed by the protection on the LV side); • it must not trip during the inrush phase of the transformer; • it must not interfere with the MV protection owned by the distribution Authority.

Restricted Earth Fault

 The example of Figure 3 shows a plant, comprising: - a protection circuit-breaker on the MV side, equipped with REF542 protection and control unit; - a MV/LV distribution transformer (with a TN-S distribution system on the LV side); - a main LV circuit-breaker type Emax equipped with PR123 LSIG trip unit; - different moulded-case circuit-breakers to protect the outgoing feeders towards the loads. In order to guarantee proper coordination and protection against the earth faults which can occur in the plant of the figure, it is necessary that: - in case of earth fault in the part of the plant between the transformer and the Emax circuit-breaker (that is in case of restricted earth fault), the MV circuitbreaker opens (afterwards it is possible to choose whether to keep the LV circuit-breaker closed or to open it);

 Company product range

----------------------Ruichang Mingsheng Automation Equipment Co., Ltd----------------------

PLC module, programmable controller, CPU module, IO module, DO module, AI module, DI module

Network communication module,

Ethernet module, motion control module, analog input module, analog output module, digital input module, digital output

Module, redundancy module, power module, relay output module, relay input module, processor module