Vacuum Circuit Breaker Switching Research Articles

Investigation on Reignition Probability of Switching Overvoltage Caused by Vacuum Circuit Breaker in Offshore Wind Farms

The reignition probability of switching overvoltage caused by vacuum circuit breaker (VCB) switching off shunt reactor (SR) in offshore wind farm (OWF) is studied. Firstly, a model of OWF is developed in the environment of electromagnetic transient program. According to the switching time of VCB, a current period is divided into non-reignition zone, reignition zone and current chopping zone. Based on the analysis of overvoltage mechanism, a method for calculating critical arcing time and reignition probability is proposed. Then, the effects of resistor-capacitor (RC) snubber on reignition probability are discussed. The capacitance of RC snubber is optimized based on switching dispersibility of VCB and critical arcing time, and a new structure of RC snubber is developed. Finally, the hybrid method of RC snubber with new structure and phase-controlled switching is presented to suppress the switching overvoltage. The results indicate that the method can eliminate the reignitions and weaken the impact of overvoltage on the insulation of power apparatus.

Investigation on overvoltage caused by vacuum circuit breaker switching off shunt reactor in offshore wind farms

The multiple reignitions of vacuum circuit braker (VCB) while switching off the shunt reactor in an offshore wind farm (OWF) would produce a high overvoltage. The post-arc process of ion movement in the vacuum interrupter is analysed. Considering the sheath growth and ion concentration variation, the expression for dielectric recovery strength inside the VCB interrupter is derived. A novel VCB model is implemented in the environment of electromagnetic transient programme based on the new reignition criterion. Then, the switching overvoltage is computed and analysed in detail. For the OWF with high rising rate of transient recovery voltage, the sheath growth must be considered in the VCB model; otherwise, the overvoltage may be underestimated. Using resistor–capacitor (RC) snubber, a new installation scheme is proposed to suppress the overvoltage in the OWF. The results indicate that the proposed scheme can not only reduce the peak and steepness of overvoltage but also damp the high-frequency oscillation. It would not affect the steady-state operation of OWF. Besides, the capacitor of RC snubber normally does not bear the electric stress, and its life expectancy would be greatly enhanced.

Three-phase modeling of 40.5-kV vacuum circuit breaker switching off shunt reactors and overvoltage suppression measure analysis

Shunt reactors are commonly used in substations to compensate the capacitive reactive power of electric power systems. When a vacuum circuit breaker (VCB) switches off shunt reactors, an overvoltage with high amplitude and high frequency (HF) is generated because of the current chopping and multireignition of the VCB. The objective of this paper is to build the 40.5 kV statistical VCB model, simulate the overvoltage caused by switching off shunt reactors in a 35 kV substation, and analyze the impact of five types of overvoltage suppression measures under identical VCB conditions and substations. The statistical VCB model is established in MATLAB/Simulink and verified by the field tests. Three basic factors are considered in this model: chopping current value, dielectric dynamic insulation strength and HF current quenching capability of the VCB. The simulation results show that the suppression effects in descending order are the phase-controlled VCB, adding surge arresters, adding RC snubbers, double-break VCB and increasing the cable length.

Suppression Measures for Overvoltage Caused by Vacuum Circuit Breaker Switching Off 10-kV Shunt Reactor

During the process in which a vacuum circuit breaker (VCB) switches off the shunt reactor (SR), an overvoltage with high amplitude and high frequency (HF) will occur because of current chopping and multireignition. To reproduce this switching overvoltage faithfully, the voltage and current characteristics of the VCB were analyzed in this work, based on the field test data from a 220-kV substation in Chongqing, China. Then, typical parameters of three basic factors mentioned in Helmer's VCB model, chopping current value, dielectric dynamic insulation strength, and HF current quenching capability, were selected after statistical analysis and an arc reignition model of VCB was established. Based on this presented model, the influences of the surge arrester, the resistor–capacitor (RC) snubber, and the installation positions and quantities of these protective devices on overvoltage suppression performance were studied in simulation. In addition, the field test using the surge arrester and the RC snubber as the suppression measures was performed again in the same substation. Finally, we derived the conclusion that the most suitable suppression scheme for overvoltage caused by VCB switching off 10-kV SR is installing two 12/32.4 kV surge arresters at the terminals of the cables for the SR and the substation transformer (ST).

Experimental Evaluation of Switching Induced Transformer Resonance Mitigation

Vacuum circuit breaker switching induced transients can cause frequency induced medium voltage transformer dielectric damage, where the two are coupled with short cable. The most common mitigation method is to add a resistor/capacitor snubber at the transformer terminals. While this approach has proved highly effective, there is little discussion of variations on the snubber application. This paper describes the results of switching tests of a vacuum circuit breaker connected to a 1-MVA transformer through medium voltage cable. First, the mechanism was investigated. The tests show the resonance is induced by the broadband frequency content due to the high dv/dt of the circuit breaker current chopping and the chopping rate. Next, snubber performance at various circuit locations was tested. The snubber was most effective at the transformer medium-voltage terminals and at the load side of the circuit breaker.

Grid connected photovoltaic power plants: new aspects in switching procedures with vacuum circuit breakers involved

This study presents vacuum circuit breaker switching investigation on a grid connected photovoltaic power plants. The focal point of this research is to discuss potential overvoltages during various switching operations in terms of the medium-voltage insulation coordination procedure. Influence of the LC filters of solar converters on high-frequency transients was highlighted, with main focus on generation of arc re-strikes and pre-strikes during opening or closing of the vacuum circuit breaker. Scheduled and emergency switching operations were analysed by means of laboratory experiments and Power Systems Computer Aided Design (PSCAD) simulations. Alternative switching sequences were proposed for mitigation of transient overvoltages.

The ITER Central Solenoid Module final test facility

General Atomics (GA) is currently fabricating the ITER Central Solenoid Modules (CSM) under contract to US ITER at Oak Ridge National Laboratory, under the sponsorship of the Department of Energy Office of Science. The contract includes the design and qualification of manufacturing processes and tooling necessary to fabricate seven CSM (6+1 spare) that constitute the ITER Central Solenoid. The modules will be produced and delivered to the ITER site during 2018–2021.Each CSM will undergo final testing at GA to verify performance. Testing includes helium leak testing, high voltage insulation testing, cooldown to 4.5K and charging to 48.5kA followed by a series of tests designed to measure as-built performance of the superconductor.GA has completed the design and is now installing and commissioning the Final Test Facility at the CSM Manufacturing site in Poway, California. The facility includes a number of critical subsystems. The test chamber system consists of a 160m3 liquid nitrogen shielded cryostat to support the 110-t CSM, a vacuum pumping and leak detection system and Paschen testing equipment. The feeder system connects the test chamber to the cryogenic and electrical systems. It includes a coil termination box (CTB), high temperature superconducting current leads and a superconducting feeder duct. The cryosystem provides refrigeration and circulates supercritical helium at 4.5K for cooling the CSM and 50K helium gas for cooling the current leads. The electrical system includes a DC power supply providing 48.5kA of current and a fast discharge system used for quench protection. The fast discharge system uses redundant DC breakers based on vacuum circuit breaker switching and a 1 Giga-Joule discharge resistor to absorb the stored energy in the coil with a 6s decay time.

Simulation of switching overvoltages in the mine electric power supply system

Overvoltages occur in mine power supply systems during switching off consumers with high inductive load, such as transformers, reactors and electrical machines. Overvoltages lead to an increase of insulation degradation rate and may cause electric faults, power outage, fire and explosion of methane and coal dust. This paper is dedicated to simulation of vacuum circuit breaker switching overvoltages in a mine power supply system by means of Simulink MATLAB. The model of the vacuum circuit breaker implements simulation of transient recovery voltage, current chopping and an electric arc. Obtained results were compared to available experimental data.

Vacuum Circuit Breaker Transients During Switching of an LMF Transformer

Switching transients associated with circuit breakers have been observed for many years. With the widespread application of vacuum breakers for transformer switching, recently, this phenomenon has been attributed to a significant number of transformer failures. Vacuum circuit breaker switching of electric arc furnace and ladle melt furnace (LMF) transformers raises concern because of their inductive currents. High-frequency transients and overvoltages result when the vacuum breaker exhibits virtual current chop and multiple re-ignitions. This paper will present a detailed case study of vacuum breaker switching of a new LMF transformer involving current chopping and restrike simulations using the electromagnetic transients program. A technique that involves a combination of surge arresters and snubbers will be applied to the LMF to show that the switching transients can be successfully mitigated. Additionally, some practical aspects of the physical design and installation of the snubber will be discussed.

Investigation of the circuit breaker reignition overvoltages caused by no‐load transformer switching surges

AbstractWhen an unloaded transformer or motor is switched under certain conditions, the circuit breaker can be exposed to a re‐strike effect that leads to voltage escalation. The effect of reignition depends not only on the type of circuit breaker, but also on the surrounding network.In this paper we describe a detailed model of all system components, which is extended where necessary, for the calculation of transients caused by the vacuum circuit breaker switching surges. Especially the transformer modelling is explained in detail for a broad frequency range because of a very complex transient behaviour. The system configuration consisting of a circuit breaker, a cable, a transformer and arresters is observed and modelled by means of some provided measured data. The results of some models are compared with measurements. The models have been imbedded into the Alternative Transient Program (ATP). The program developed here can be widely used for studies of transient recovery overvoltages caused by interruption of transformer steady‐state and inrush currents if the measured data and parameters for the system components are known.

Instrumentation for High-Speed Digital Recording of Switching Surges

Three sophisticated monitoring systems were developed and used to make unattended measurements of over 600 switching surges on 33 motors at 11 different utilities. The authors describe in detail one of the recording systems which relies on ECL (emitted coupler logic) digital electronics and high-speed commercial digitizers to measure the multiple, fast-risetime, high-voltage surges typically created by vacuum circuit breaker switching operations. This three-channel monitoring system is capable of digitizing a voltage waveform at 5 ns intervals and has 64 K bytes of memory per channel. The digitizer sampling rate is varied in real time to allow high-speed recording of up to 256 transients. Wideband capacitive voltage dividers with a flat response from below power frequencies to 20 MHz were designed to bolt directly onto the motor terminals and were used to couple the surges to the monitoring system. Results from typical field measurements made with this system on motors controlled by vacuum switchgear are also reported. >

Field Testing of Voltage Transients Associated with Vacuum Breaker No-Load Switching of a Power Transformer in an Industrial Plant

Reported here are the results of a field investigation of switching-produced transients associated with vacuum circuit breaker switching of an unloaded low-voltage substation transformer. A sufficient sampling of data has been obtained and documented to provide a good statistical basis for this important mode of switching in a very prevalent application area. The results of this field measurements program confirm that the transient voltage environment created by such switching is within, by a wide margin, the expected transient capabilities of the associated power distribution equipment?specific evaluation being made with respect to the switched transformer.