Introduction to Earth Leakage Relays.
Earth leakage relays perform two main functions on mining installations: to protect machinery from damage and to make the installation safer for personnel. In the typical distribution circuit shown in Fig 1, an earth leakage relay provides protection against leakage to earth and earth faults. The principle of this method is that all the current flowing to the load must return from the load. If current leaks to the frame of the motor and returns via the earth bond back to the star point of the supply transformer then this difference is detected by the earth leakage relay which triggers the breaker, thus disconnecting the load.
It becomes apparent that the earthing must be solid and reliable for electrical installations to be safe. For this reason, machinery is earthed via the supply cable, using either a copper conductor of the cable or the armour. The ground on which the machinery stands is normally not considered a reliable earth. Mechanical damage to the earth bond, corrosion of the armour or bad workmanship may result in a high resistance point in the earth return. If an earth fault occurs, voltage will be developed across the high resistance region. This voltage poses a potential hazard to any personnel who may be exposed to it. Depending on the resistance value, the current flowing and the reaction time of the earth leakage relay, this could be fatal. It is obvious that continuous monitoring of the earth bond is imperative if safety standards are to be maintained.
SWITCHING SYSTEMS' range of EARTH CONTINUITY RELAYS provides a cost effective solution to the problem.
SWITCHING SYSTEMS' Earth Continuity Monitors are grouped into two categories:
PILOT WIRE CONTROL RELAYS, prefixed GBP, MP & MSR. These relays offer simple and cost effective solutions. They have remote stop/start capability. The maximum resistance level is permanently set at 22Ω for GBP/MP relays, and at 100Ω for MSR Relays. They are used primarily underground with short cables and medium power loads.
Three generations of relays are available:
• The first, MSR8-
• The second, MSR9-
• The third, MP130-
EARTH CONTINUITY RELAYS, prefixed GCM.
This relay is micro-
ECR Range>Earth Leakage Relays