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High Power Batteries as Power Source with Dynamic Resistance Measurement and Both Sides Grounded

Abstract

The arcing contacts are the most important parts of a high voltage circuit breaker (CB). One of the most elegant methods used to detect the condition of the arcing contacts is the Dynamic Resistance Measurement (DRM). It consists of injecting high direct current (DC), order of 100-200 A or even with 500A as reported by Mrdic in [1], through the circuit breaker main circuit and measuring the voltage drop (using Kelvin’s four-point method) during the breaker operation. This principle is also used for measurement of the main contact resistance. Additionally, it is used during timing tests to detect the instant of the separation and touch of the arcing contacts, in conditions when both sides of CB are grounded (BSG – Both Sides Grounded).

DV Power researched the power source that provides high impulse DC current in the form of the High Power batteries. These batteries have higher capacity than supercapacitors (whose usage was already reported for this purpose) and low demand for recharging. At the same time, they are suitable for the installation in a portable test instrument. In addition, these batteries are approved for air transportation. The solution applying the current regulator, including use of the High Power batteries as a power source for Dynamic Resistance Measurement and Both Sides Grounded methods is described in this paper. Also, test results of Dynamic Resistance Measurement and Both Sides Grounded methods using this particular power source by DV Power instruments will be presented and discussed.

Scheme of Dynamic Resistance Measurement on One Side Grounded and Both Sides Grounded Circuit Breaker
Figure 1: Circuit Breaker Test with One Side Grounded (left) and Both Sides Grounded (right)

Intro

Electrical arc phenomena have been studied for a long time. It is an inevitable process that occurs during interruption of high electrical currents (e.g., during a short circuit current interruption). The effects of the electrical arc on the circuit breaker contacts are known, and great attention has been paid to developing methods to analyze arc behavior and minimize damage to the breaker contacts.

One mitigating solution is the separation of main and arcing contacts. Arcing contacts are responsible for carrying the arc inside the breaker chamber during the breaker operation. These contacts must be designed to withstand high currents and high temperatures with minimal deformation and erosion. The real challenge is to learn about the state of these contacts during regular maintenance procedures. The goal is to reduce the time spent on testing to bring down maintenance costs and keep equipment out of operation as briefly as possible. The arcing contacts are active (carrying current) only a few milliseconds. Thus, the test and the collection of useful data set must be adjusted to this very limited time frame.

Dynamic resistance measurement (DRM), already adopted and approved as the standard testing procedure by many maintenance companies, is usually based on recording a resistance and a motion curve during the opening operation of the high-voltage circuit breaker.

However, by recording a dynamic resistance curve during the closing operation of the breaker, the useful data set can be extended. Consequently, the diagnostic process is more reliable. The circuit breaker arcing contact is the first to make contact during a closing operation and the last to break contact during the opening. Therefore, arcing contact wear occurs during normal operation as well as when interrupting fault currents. If the arcing contacts are damaged, the breaker becomes unreliable very quickly. An important diagnostic parameter is the main circuit resistance of the circuit breaker. This parameter is measured while breaker main contacts are in a closed position. For that reason, measurements can be recorded just before or after the Dynamic Resistance Measurement with the procedure, which reduces testing time since both measurements can be performed in one test sequence.

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July 9, 2019

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