**Comparators in Power System:**

**Coincidence Type Phase Comparator**** :** The basic concept of phase comparison is simpler in that it is possible to deal with signals of equal strength whose coincidence (or noncoinecidence) is readily measurable. Considering two sinusoidal signals S1 and S2, the period of coincidence of S1 and S2 will depend on the phase difference between S1 and S2. Figure (11.14) illustrates the coincidence of signals for different phase relationships in Coincidence Type Phase Comparators in Power System. It can be seen that the period of coincidence is equal to the period of noncoincidence for a phase difference of ±90°,the period of coincidence is less than the period of noncoincidence and vice versa when the phase difference is less than ±90°. Depending upon the phase relation of the input signals it is possible to design the circuit to give an output a Yes or a No, by measuring the period …

**Phase Comparator Circuit**** :** Phase Comparator Circuit technique is the most widely used for all practical directional, distance, differential and carrier relays. If the two input signals are S1 and S2 the output occurs when the inputs have a phase relationship lying within specified limits. Both inputs must exist for an output to occur; ideally, operation is independent of their magnitudes, and is dependent only on their phase relationship. Fig. (11.13) illustrates the Phase Comparators in Power System Circuit in its simple form. The function as defined by the boundary of marginal operation is represented by two straight lines from the origin of the complex plane. The condition of operation can be put mathematically as where θ is the angle by which S2 leads S1. If β1=β2=90° the comparator is known as cosine comparator and if β1=0 and β2=180° it is a sine comparator. Static Phase Comparator Circuits may be of …

**Static Amplitude Comparator**** :** If the two input signals are S1 and S2 the amplitude comparator gives positive (yes) output only if S2/S1 ≤ K (Fig. (11.1)), S1 is the operating quantity and S2 is the restraining quantity. Ideally, the comparison of the two input signals is independent of their level and their phase relationship. The function is represented by a circle in the complex plane, with its centre at the origin: this defines the boundary of the marginal operation. Static Amplitude Comparator may be of the following types: Integrating comparators, Instantaneous comparators, and Sampling comparators. Integrating Comparators: It is possible to arrange rectifier bridge networks as amplitude comparators. Rectifier bridge comparator can either be of circulating current type or opposed voltage type. Basic circuit for the circulating current type of Static Amplitude Comparator is shown in Fig. (11.2). The polarized relay operates when S1>S2, where S1=K1i1 and S2=K2i2. …