Adaptive Impedance Relay with Composite Polarizing Voltage
Fault resistance can bring some disadvantages for an impedance relay while a single-phase-to-ground fault occurs on transmission line. Taking advantage of the compensated voltage changing with fault resistance, this paper presents a kind of adaptive impedance relay with composite polarizing voltage to enhance the capability against fault resistance. On the other hand, the operating boundary of the adaptive relay may enter into "in-phase" region along with the increase of fault resistance. To prevent the adaptive relay from the "in-phase" problem, a new additional blocking component is proposed in this paper. Both the adaptive relay and the blocking component are all analyzed in the voltage plane and the impedance plane. Theoretical analyses show that both of them have circular characteristics with greater resistive tolerance. The performance of the relay has been demonstrated on a two-source 500 km line 750 kV system.
Research of one new adaptive mho relay
In this paper, a new mho relay based on the adaptive principle is proposed. The operation boundary of the new relay can be adjusted to adapt different earth-fault resistance automatically, and provide consistent relay zone coverage. Therefore the adaptive mho relay has a perfect performance for the protection of single phase-to-earth faults, especially the high impedance faults on transmission line. The performance of the relay has been verified on a simulated network using ATP program. The result shows that the new adaptive mho relay has excellent performance within the protective zone, and it can reflect inner single-phase faults with a high impedance of more than 800 /spl Omega/ on a simulated 300 km long transmission line of 500 kV.
Fault component reactance relay
A new power system distance relay is developed in this paper. The relay is based on two operation criteria: a current criterion; and a voltage criterion. Each uses the fault component as the operating quantity, and the relay reacts only on the reactance of the transmission line. So, it is a fault component reactance relay. During external faults, the two criteria are complementary to each other, i.e. at least one of them will not be satisfied; so no maloperation will occur. During internal faults, both criteria will be satisfied even if the fault resistance is high.