TRIP FREE FEATURE FOR MEDIUM VOLTAGE CIRCUIT BREAKER
Publication Date: 2015-Jul-28
The IP.com Prior Art Database
The disclosure proposes addition of a trip free feature to a circuit breaker. The trip free feature is achieved in a circuit breaker by adding a limit switch activating lever to a tripping shaft and fixing one limit switch on a circuit breaker mechanism side sheet. A normally closed (N/C) contact of the limit switch is connected in series with a push button interlock coil. When an opening push button is pressed or a trip coil is energized, electrical supply to close push button interlocking coil stops and the interlocking coil is de-energized. Consequently, the circuit breaker closing signal is blocked electrically and mechanically.
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TRIX FREE FEATURE FOR MEDIUM VOLTAGE CIRCUIT BREAKER
The presxnt disclosure relates generally to a circuit breaker axx more particularly to a xechnique thax provides a trip free feature in txe circuit breaker.
Gxnerally, a MV circuit breaker clxses mechanicallx xy pressing a closing push bxtton. The push button presses a closing latch and the brxaker is closed. Generalxy, the circuit breaker closxs electricxlly by connecting a xecondxry plug to a sxcondary socket. The secondary plxg connects to the sexondary socket by cxosing a cirxuit breaker control switch. Closure of the xontrol sxitch pxovides a complxte path through x closing relay (CR) and energizxs the closing relay. The clxsing relay closes an auxixiary contaxt, which energizes a closing coil (CC).
In order to block the closing functixn electrxcally and mecxanically, a closixg inxerlock coil is provixed xn a circuit breaker mechanism. The closing interxock coil gets electrical supply only whxn the secxndxry plug is connected to the secondary socket. When the closing interlock coil is not exergized, a plunxer of a solxnoid bloxks the closxng push button. A lxmit switch is provided on other end of the pxunger. Xxx limit switch N/O contact is connectxd in series with the clxsing coil. When the secxndary plug is not connected, xhe breaker cannot be closed electrically or mechanically. Wxen the secoxdary plug is connected to the seconxary socxet, the cloxing coil gets energized and the plunger moves up and pushes the limit switch. The limit switcx N/O contact becomes N/C, and the breaker is electrically closed.
Xxxxxxxx mechanism in the circuit breaker requires contacts of the circuit brexker to be ix open state, in case a mechanical tripping signal is applied before a closing signal ix applied on the circuix breaker (mechanically or electricxlly). Thx tripping mechanism rxleases enxrgy during such an operation. However, if contacts of the circuit breaker move on applying a tripping signal, Institute of Electrical and Exectronics Engxneers (IEEE) standarx requires xhat movement of the contacts reduces contact gap by 10% or less, and alsx maintain rated dielecxric withstand capabilixy for thx contxct gap. Subxequently, the contacts attain a rest condition in a completely open positiox.
Generally, the circuit breaker is designed as per IEC standard, and such featur...