Method and device for determining ground faults on the conductors of an electrical machine
AssigneeABB Management AG
InventorMichael Pfiffner
Life of this patent
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Abstract
A method is specified for detecting ground faults on the conductors of electrical machines, in which method the fault resistance (Rf) is directly calculated in a numerical evaluation unit (7) from the injected (Ui) and the measured (URE) voltages. Since the fault resistance is explicitly calculated and displayed, it is independent of influences from the ground reactance. Moreover, there is no need to, for each machine, characteristics for drawing conclusions on the fault resistance. Moreover, the influence of ageing, temperature fluctuations, injection level fluctuations etc. is eliminated due to the numerical calculation. (FIG. 1a)
Claims6
A method for detecting ground faults on conductors of an electrical machine, the method comprising the steps of:
- a) biasing the conductors with respect to ground potential by means of a low-frequency injection voltage U.sub.i of frequency f.sub.1, and measuring and evaluating a measuring voltage U.sub.RE via a ground resistor R.sub.E connected to the conductors;
- b) calculating a ground fault resistance R.sub.f from the injection voltage U.sub.i and the measuring voltage U.sub.RE, and numerically displaying said ground fault resistance R.sub.f in a numerical evaluation unit connected to the measuring voltage;
- the conductors being the stator windings of said electrical machine connected in star;
- c) dividing the injected and measured voltages U.sub.i and U.sub.RE in the evaluation unit into orthogonal components U.sub.ix, U.sub.iy, and U.sub.REx, U.sub.REy, respectively;
- and
- d) calculating the ground fault resistance R.sub.f in the evaluation unit in accordance with:
- ##EQU6## .
A method for detecting ground faults on conductors of an electrical machine, the method comprising the steps of:
- a) biasing the conductors with respect to ground potential by means of a low-frequency injection voltage U.sub.i of frequency f.sub.1, and measuring and evaluating a measuring voltage U.sub.RE via a ground resistor R.sub.E connected to the conductors;
- b) calculating a ground fault resistance R.sub.f from the injection voltage U.sub.i and the measuring voltage U.sub.RE, and numerically displaying said ground fault resistance R.sub.f in a numerical evaluation unit connected to the measuring voltage, the conductors being the rotor windings of said electrical machine and said injection voltage U.sub.i being fed into the terminals of the rotor windings via coupling capacitors;
- c) dividing the injected and measured voltages U.sub.i and U.sub.RE in the evaluation orthogonal components U.sub.ix, U.sub.iy, and U.sub.REx, U.sub.REy, respectively;
- and
- d) calculating the ground fault resistance R.sub.f in the evaluation unit in accordance with:
- ##EQU7## where U.sub.Ckx and U.sub.Cky represent orthogonal components of a voltage U.sub.Ck measured over said coupling capacitors.
Dependencies are inferred from the claim text.