Abstract
This paper proposes a simple and fast way to determine the direction of a fault in a multi-terminal high voltage direct current (HVDC) grid by comparing the rate of change of voltage (ROCOV) values at either side of the di/dt limiting inductors at the line terminals. A local measurement based secure and fast protection method is implemented by supervising a basic ROCOV relay with a directional element. This directional information is also used to develop a slower communication based DC line protection scheme for detecting high resistance faults. The proposed protection scheme is applied to a multi-level modular converter based three-terminal HVDC grid and its security and sensitivity are evaluated through electromagnetic transient simulations. A methodology to set the protection thresholds considering the constraints imposed by the breaker technology and communication delays is also presented. With properly designed di/dt limiting inductors, the ability of clearing any DC transmission system fault before fault currents exceeds a given breaker capacity is demonstrated.
Highlights
In order to reduce the impact of electricity generation on alarmingly unfolding climate change, policies have been implemented to increase the use of renewable energy resources for bulk electricity generation
The communication assisted rate of change of voltage (ROCOV) based directional comparison scheme proposed in this paper can be designed to clear high resistance faults before fault currents exceeds the DC breaker limit
It is demonstrated that entire spectrum of fault resistances can be covered by using the proposed local measurement based directional ROCOV relay in parallel with a communication assisted two-end ROCOV relay
Summary
In order to reduce the impact of electricity generation on alarmingly unfolding climate change, policies have been implemented to increase the use of renewable energy resources for bulk electricity generation. A method to identify the direction of a fault using local measurements and a basic arrangement to use the identified fault directions to improve the sensitivity, speed and reliability of the ROCOV based HVDC grid protection scheme described in [9] are presented. Discrimination of high resistance faults at the far end of a long cable or transmission line is challenging [22] To overcome such situations, a double ended ROCOV based directional comparison scheme is presented. It was assumed that basic fault protection is provided using the ROCOV based protection proposed in [9] In this scheme, each line/cable section is protected using DC circuit breakers, and di/dt limiting inductors ( referred to as terminal inductors) placed at either end [24]. The PSCAD surge arrester model with default characteristic and 243 kV rating was used in the hybrid breaker circuit
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