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CONTEMPORARY MODHUB-16E module

The limit curve for Westinghouse machines is given in Fig. 3.5.23.1. The operating characteristic of the U/f-Inv protection function should be selected to be just below the short-time limit curve for overfluxing. The time limits t-min and t-max must also be set (see Fig. 3.5.23.2). It must also be noted that depending on the standard or specification, the units are also designed for a continuous level of overfluxing apart from the short-time level. Typical values for generators would be 100, 105, 107.5 and 110%. The choice of characteristic must also take the continuous level of overfluxing into consideration

Ground fault protection function for detecting ground faults close to the star-point of a generator. The scheme is based on the principle of displacing the potential of the generator star-point by injecting a coded low-frequency signal. The injection signal is generated by the injection unit REX 010 and fed into the stator circuit by the injection transformer block REX 011. This protection in conjunction with the voltage function 'Voltage', which covers 95 % of the winding, achieves detection of ground faults over 100 % of the winding. Compensation is provided for the influence of a second high-resistance grounded star-point in the zone of protection. Stator ground faults producing a current at the star-point > 5 A cause the P8 contactor to reset which separates the injection unit Type REX 010 from the injection transformer block REX 011 and interrupts injection in both stator and rotor circuits. In this case the 95 % stator ground fault protection takes over the job of clearing the fault on its own.

Inputs and outputs

protects the star-point and a part of the stator winding depending on the ground fault current
displacement of the star-point in relation to ground by injecting a signal generated by the injection unit REX 010
computes the ground fault resistance
monitors the amplitude and frequency of the injection signal
monitors the measuring circuit with respect to open-circuit and correct connection of the grounding resistor III. Binary outputs:
alarm stage pick-up
alarm
trip stage pick-up
trip
2nd. parallel star-point
MTR adjustment active
REs adjustment active
injection open-circuit internally
injection open-circuit externally. IV. Measurements:
ground fault resistance Rfs
measurement transformer ratio MTR"
grounding resistor REs". Explanation of measurements: Rfs: Ground fault resistances between 0 and 29.8 k can be determined and displayed. A display of 29.9 k or 30 k indicates a ground fault resistance >29.8 k. A value of 29.9 k or 30 k is displayed when there is no ground fault. A whole number between 100 and 111 is displayed for the fault code in cases when it is not possible to compute the ground fault resistance.
100.0 means no injection for more than 5 s.
101.0 means incorrect frequency. Either the injection frequency on the REX 010 or the rated frequency on the RE. 216 is incorrectly set.
102.0 means external open-circuit.
109.0 means that both the binary inputs 'AdjREsInp' and 'AdjMTRInp' are enabled.