The main products

Spare parts spare parts, the DCS control system of PLC system and the robot system spare parts,

Brand advantage: Allen Bradley, BentlyNevada, ABB, Emerson Ovation, Honeywell DCS, Rockwell ICS Triplex, FOXBORO, Schneider PLC, GE Fanuc, Motorola, HIMA, TRICONEX, Prosoft etc. Various kinds of imported industrial parts

UFC721BE101 3BHE021889R0101 Control module

A further difference lies in the fact that the "a" factors only effect the differential protection, whilst changing the reference values of the A/D channels effects the currents for the entire protection system (all functions and measured variables). The windings of a three-winding transformer normally have different power ratings and a reference power has to be chosen, which is used for all three windings. All the settings of the protection are then referred to the reference currents calculated from the reference power.Assuming the reference power SB to be 25 MVA, the reference currents IB and the "a" factors become:A further possibility of compensating different rated powers in the case of three-winding transformers is to use
the reference values of the A/D channels to match the protection to the different rated currents of c.t's and transformer
factors a1, a2 and a3 to compensate the different powers of the windings. The "a" factors compensate the signals at the inputs of the differential protection. If the reference values of the A/D channels are changed, the changes apply to the entire protection system (i.e. all functions and measured variables). This can be seen from the following example

C.t's in the unit transformer feeder 

When designing the overall differential protection for a generator/transformer unit, there are the following alternative methods of taking account of the c.t's or lack of c.t's in the unit transformer feeder (Fig. 3.5.2.4). Alternative No.1: No c.t's in the unit transformer feeder. This alternative is mainly needed for hydroelectric power plants, which have a relatively low auxiliaries requirement. The disadvantage is that the zone of protection is unlimited in the direction of the unit transformer feeder with the possible hazard of false tripping for a fault on the unit auxiliaries supply system. This hazard can be avoided by correspondingly setting "g

It follows from this that "g" must be set higher than 0.3 to avoid the possibility of a false trip. Alternative No. 2: C.t's installed in the unit transformer feeder on the generator side of the unit transformer (Fig. 3.5.2.4). These c.t's usually have the same ratio as the generator c.t's although the rating of the unit transformer is much less. The reason is the high fault level on the generator side of the unit transformer and the consequentially high thermal and dynamic stress on the c.t's. The reference value of the c.t. channel of the protection is determined by the rated current of the generator and not of the unit transformer. Alternative No. 3: C.t's installed in the unit transformer feeder on the auxiliaries side of the unit transformer (Fig. 3.5.2.4). In this case, the c.t's are specified according to the rated current of the unit transformer. Advantages:
clearly defined zone of protection
reduced performance required of the c.t's, which are therefore cheaper. Disadvantages:
Interposing c.t's may be necessary.
reduced sensitivity of the protection for faults in the protected zone, but on the auxiliaries’ side of the unit transformer.