LIM product page.
The LIM2 has been brand labelled for Eaton Corp. as the D64L2.
Ungrounded systems are commonly called ‘floating’ or ‘IT’ electrical systems. ‘IT’ stands for Isolated Terra. The secondary of a three-phase delta connected transformer is typical of this type of system.
It is generally accepted that on installations using ungrounded electrical supply systems, protection against electrical shock cannot normally be provided by the use of conventional ground fault relays (GFRs) or residual current detectors (RCDs). Leakage currents to ground require a return path. Therefore, when no such path exists, a standard GFR or RCD would be unable to detect a fault when it occurs.
The solution to this problem is the LIM, Line Insulation Monitor. The LIM sequentially monitors each
phase of the single- or three-phase ungrounded AC power system, 380 to 600 V on systems with a
frequency of 50 – 60 or 400 Hz. If an insulation fault develops anywhere on the system between the
source and the load, a small current will flow through the high impedance of the unit. This current is
analysed by the LIM and it will alarm or trip depending on the selected settings.
The detection circuitry is based on impedance measurement of the monitored system.
The LIM is NOT designed to discriminate between different circuits fed from the same source of supply. Therefore, it is ideal for monitoring a system supplied by its own isolation transformer with either an ungrounded delta or an ungrounded wye connected secondary.
Because the LIM has high immunity from the effects of voltage transients and cable capacitance, it may be applied in automotive, sub-sea, mobile lighting, portable generators, sensitive equipment and other installations where ungrounded systems are used extensively.
The LIM houses an isolated universal power supply from 24 - 240 V AC or DC and is equipped with two form ‘Z’ (4 connections) isolated NO and NC contact sets. The System Phase Configuration (3 phased or single phased), the Leakage Current Limit (20, 35 or 50 mA RMS), the Alarm and Trip relay Operating Mode (Failsafe, Non-Failsafe RRPL, Non-Failsafe Latched) and the Reset mode (manual or automatic) are set on two front accessible dipswitch arrays.
Two single turn potentiometers permit the alarm level and the trip level to be individually set from 20% - 80% of the selected maximum leakage current limit of the LIM. Any leakage current above the alarm level will activate the alarm relay and light the yellow ‘ALARM’ LED. Should the leakage current rise above the trip level, the trip relay and red ‘TRIP’ LED will activate. The fault current is measured every 70 ms. Once a fault is detected, the sampling is discontinued and the sample rate will go to approximately 2 seconds. One of three yellow LEDs (L1, L2, L3) will light to indicate the faulted phase.
To ensure that the LIM will function in all circumstances, it is encapsulated in polyurethane (PUR) to make sure it is not vulnerable to mechanical shock, vibration nor weather.
LIM product page.
The LIM2 has been brand labelled for Eaton Corp. as the D64L2.
Ungrounded systems are commonly called ‘floating’ or ‘IT’ electrical systems. ‘IT’ stands for Isolated Terra. The secondary of a three-phase delta connected transformer is typical of this type of system.
It is generally accepted that on installations using ungrounded electrical supply systems, protection against electrical shock cannot normally be provided by the use of conventional ground fault relays (GFRs) or residual current detectors (RCDs). Leakage currents to ground require a return path. Therefore, when no such path exists, a standard GFR or RCD would be unable to detect a fault when it occurs.
The solution to this problem is the LIM, Line Insulation Monitor. The LIM sequentially monitors each
phase of the single- or three-phase ungrounded AC power system, 380 to 600 V on systems with a
frequency of 50 – 60 or 400 Hz. If an insulation fault develops anywhere on the system between the
source and the load, a small current will flow through the high impedance of the unit. This current is
analysed by the LIM and it will alarm or trip depending on the selected settings.
The detection circuitry is based on impedance measurement of the monitored system.
The LIM is NOT designed to discriminate between different circuits fed from the same source of supply. Therefore, it is ideal for monitoring a system supplied by its own isolation transformer with either an ungrounded delta or an ungrounded wye connected secondary.
Because the LIM has high immunity from the effects of voltage transients and cable capacitance, it may be applied in automotive, sub-sea, mobile lighting, portable generators, sensitive equipment and other installations where ungrounded systems are used extensively.
The LIM houses an isolated universal power supply from 24 - 240 V AC or DC and is equipped with two form ‘Z’ (4 connections) isolated NO and NC contact sets. The System Phase Configuration (3 phased or single phased), the Leakage Current Limit (20, 35 or 50 mA RMS), the Alarm and Trip relay Operating Mode (Failsafe, Non-Failsafe RRPL, Non-Failsafe Latched) and the Reset mode (manual or automatic) are set on two front accessible dipswitch arrays.
Two single turn potentiometers permit the alarm level and the trip level to be individually set from 20% - 80% of the selected maximum leakage current limit of the LIM. Any leakage current above the alarm level will activate the alarm relay and light the yellow ‘ALARM’ LED. Should the leakage current rise above the trip level, the trip relay and red ‘TRIP’ LED will activate. The fault current is measured every 70 ms. Once a fault is detected, the sampling is discontinued and the sample rate will go to approximately 2 seconds. One of three yellow LEDs (L1, L2, L3) will light to indicate the faulted phase.
To ensure that the LIM will function in all circumstances, it is encapsulated in polyurethane (PUR) to make sure it is not vulnerable to mechanical shock, vibration nor weather.