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.
Study on Adaptive Ground Distance Relay
One of the critical problems that need to be solved by a ground distance relay is to improve the capacity of the earth-fault resistance endurance of the relay. The modification of adaptive operating characteristic, based on the analysis of adaptive operation characteristic of current adaptive ground distance relay, is proposed. The modified adaptive ground distance relay can effectively avoid transient-state overreach, and reflect the earth-fault up to a super high resistance. Simulations show that the proposed new adaptive ground distance relay has excellent adaptability and selectivity.
A novel algorithm for high-resistance earth-fault distance protection
The steady-state operating characteristic of earth-fault distance protection based on a differential equation is analyzed. It is shown that this system may either over-reach or under-reach at some power system operating conditions. A novel algorithm for high-resistance earth-fault distance protection is put forward. Theoretical analysis and digital simulation results show that this new algorithm can overcome the steady-state over-reach problem with excellent reach accuracy and operating time.