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CI541V1 3BSE014666R1 Control module card

When a motor or generator is stationary, there is no forced cooling and the cooling time constant is much longer. The time constant at standstill is defined by the setting of the factor "k". The time constant is switched when the current falls below a given value and the external signal "Stillst.-Inp" is being applied at the same time. The universal model enables overtemperature to be monitored on the basis of a general function, which describes the temperature rise for a given current change. Fig. 3.5.19.1 shows the response of the general function s (t) to a step change in the current. The general function s (t) is divided into 40 sections. The mean values h1, h2 ... h40, which define the steps of the impulse response, are determined graphically from the derivation of the function s (t) for the individual sections in relation to time. These instantaneous values of the impulse response are entered as h[1] to h[40] when using the universal model. The "ResponseTime", i.e. the duration of the impulse response, must also be entered. Zero must be entered for the thermal time constant "TimeConstant". The reduced cooling of a motor or generator at standstill is taken into account by extending the impulse response by the factor "k" when an external signal coincides with operation of the low-current monitor.

frequency protection

Over/underfrequency MaxMin A frequency function is used to protect synchronous generators and prime mover against variations of speed and also in the underfrequency mode in load shedding schemes. The frequency function protects:
synchronous generators against excessive temperature rise due to increased iron and other losses
synchronous generators and prime movers against damage due to vibration. Many synchronous machines are subject to severe vibration when operating at speeds other than rated speed. Vibration is particularly pronounced when underspeeding, but can occur both at under and overspeed. For this reason, a frequency scheme will usually include two stages for alarm and tripping at overspeed and two stages for alarm and tripping at underspeed. A time delay confines the danger of false tripping during transients.