switchgear interlock and safety features

SWITCHGEAR INTERLOCKS AND SAFETY 

FEATURES

INTRODUCTION

Interlocks and safety features on switchgear are for the purpose of protecting both operating personnel and the equipment from physical harm. It is therefore, important to remember that an INTERLOCK or SAFETY FEATURE should never be bypassed of defeated. 

The various mechanical and electrical interlocks and safety features to be described below will be described literally not physically. To determine the physical description, 

the appropriate instruction book should be referenced. The described list can be found in part or in total on various types of switchgear. To determine which of these features are associated with a piece of equipment, the operating instruction of that equipment should be referenced. 

MECHANICAL

POSITIVE INTERLOCK

This interlock mechanically couples the breaker so that the racking mechanism can only be engaged if the breaker is in the OPEN position. This interlock prevents inserting or removing a closed breaker. 

NEGATIVE INTERLOCK

This interlock mechanically places the breaker's trip shaft in a tripped position, and thus prevents closing a breaker in any position other than TEST or CONNECTED after the racking mechanism has been disengaged. 

SPRING DISCHARGE INTERLOCK

This interlock will discharge the closing springs to provide a mechanical safety feature so that a breaker is DISCHARGED as well as open when it is removed from the equipment. 

GE Power VAC switchgear is designed to discharge the springs anytime the breaker is moved from one position to another for enhanced safety. 

PADLOCKS

Provisions are provided on either the breaker or the racking mechanism to enable the breaker to be locked out during certain operations or maintenance. 

The padlocking can either prevent closing the breaker and/or prevent engaging the racking mechanism. 

KEY INTERLOCKING

This feature allows the coordination between two or more DEVICES so that certain operations must be performed to one device before proceeding to operate the next device. 

The above coordination is accomplished by special locks, which hold the key captive until the proper conditions are met. When the conditions are met the key can be removed and inserted into another special lock on another device in order to properly operate it.

SAFETY ROLL-IN STOP

Regardless of the position of the racking mechanism, it is impossible to manually insert the breaker into the rails beyond the disconnect / test position. 

SAFETY ROLL-OUT STOP

This safety stop prevents the breaker front being rolled out of the equipment accidentally. 

This stop has to be manually released prior to breaker removal onto the transfer truck.

 

GAG SPRING INTERLOCK

While the closing spring may have been gagged for breaker adjustments, 

without this interlock it would be possible to put the breaker into operational position. 

This interlock, therefore, assures that only breakers with freely operating closing springs can be inserted into the equipment.

 

RATING INTERFERENCE INTERLOCK

This is a very sturdy mechanical interlock, which is coded so that only the properly rated breaker can be inserted into its designated location. 

ELECTRICAL 

INTERLOCK SWITCHES

The basic function of these switches is to block electrical closing signals and to open the closing mechanism's current charging circuit whenever a breaker is being inserted or removed. 

Because the electrical switches can be operated by various mechanical parts to do the same job, INTERLOCK SWITCH is a general term. To determine just which switch provides the feature, the electrical schematics should be referenced.