HIST-1 Earth-leakage monitor for trolleybuses

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Driver and passenger protection against electrical shock

The Earth-Leakage Relay HIST-1 is a device designed for continuous monitoring of isolation state during operation of trolleybuses on traction mains with the voltage rating 600 or 750 VDC.

HIST-1 continuously monitors the state of basic and auxiliary isolations of electric circuits of the trolleybus and signalises its possible deterioration under the allowed limits. By timely warning about risk of electric shock, it increases safety of passengers and the driver.

The automated isolation status control brings significant reduction in work difficulty during preparation of the trolleybus before its leaving for the line and makes the operation more efficient and safe for the whole trolleybus lifetime.

Measuring overall insulation status of vehicles

Measuring overall insulation status of vehicles

The unit is resistant to traction network polarity switching and allows measurement of the overall insulation status of the vehicle as well as the individual insulation in all types of traction networks – isolated symmetrical, isolated asymmetrical, grounded or combined networks.

The traction network type is selected by setting the central register and the unit automatically selects the corresponding method of measurement according to the network type. Therefore all the measurement methods can be performed using one device.

Unit features:

  • Measurement of vehicle insulation status using an artificial centre of traction voltage, earthed trolley wire or earth-wire
  • Exact measurement of insulation resistance values by means of a built-in 48VDC supply
  • Test and measurement of the insulation resistance by means of a built-in 1000VDC supply (simple measurement of the vehicle's state before it leaves the depot) just by one button press by the driver, the result is recorded into the unit's memory
  • Communicates with other units through state outputs, CAN or RS232 communication interfaces as required by the user.

In case of low insulation state, it records such events and saves them into the internal memory.

Adjustable measuring frequency

Adjustable measuring frequency

The Earth-Leakage Relay is designed as a numerical measuring instrument with a microprocessor control and memory of evaluated limits.

The microprocessor periodically starts measuring twelve power inputs (10 inactive parts and 2 three-phase IT mains) against two reference inputs (vehicle body and trolley wire).

All inputs are equipped with protective impedances. It allows you to measure up to 24 combinations of inputs and you can use up to four methods of measurement to evaluate the isolation state:

  • Measurement of crest voltage
  • Measurement of earth-leakage current
  • Measurement of current from the internal 48VDC power supply and computation of isolation resistance
  • Measurement of current from the internal 1,000VDC power supply and computation of isolation resistence

The period of measurement is adjustable. The measurement result for each of the power inputs is indicated by a pair of LEDs (white and red) on the front panel. The course and method of measurement are signalised by four yellow LEDs.

Stores data even during power outage

Stores data even during power outage

All adjustable parameters necessary for correct operation of the unit and measured limits are saved in three memory blocks, which keep data also in case of a voltage failure:

Memory of modes – allows you to adjust date, time and interval of measurement and to select, which methods of measurement will be used in the individual combinations of power inputs. Only authorized person can perform this change of function using a laptop.

Memory of limits – allows you to adjust two limits for each method of measurement and each combination of power inputs for signalisation (WARNING, DANGER) of their overrunning/underrunning. The adjustment of limits for signalisation can be done only by an authorised person using a laptop.

Memory of exceeded limits – records up to 128 cases of exceeded limits of voltage, current or isolation resistance incl. their numerical values and the corresponding date and time of the event. Presence of unread records in this memory is signalised by a lighting LED. After the records are loaded into the laptop, the LED gets off. If the memory is full, the oldest data are rewritten by the new ones.

Construction

Construction

The earth-leakage relay is located into one plastic box (230 x 200 x 95 mm) with a transparent door, under which there is a front panel with LEDs, two buttons and instrument terminals.

Inputs of inactive parts and electrical centres of active parts are connected to the terminals, which allows you to measure resistances of the individual isolation layers directly on them (e.g. using Megmet) when the earth-leakage relay is OFF, or to simulate reduced isolation states when the earth-leakage relay is ON.

The earth-leakage relay is connected with electrical circuits of the trolleybus by means of connectors. Their counterparts to connect wires are supplied in the accessories.