Modems help quality of electricity supply

As part of its ENIP electricity network improvement project, United Utilities is using more than 700 Westermo GSM modems.

As part of its ENIP electricity network improvement project, United Utilities is using more than 700 Westermo GSM modems to act as communications interfaces between remote secondary switchgear and its distribution control centre based in Manchester, to ensure it can meet the latest Ofgem "quality of supply" (QoS) targets.

The GSM modems are used because of the size of the region and the remoteness of the sites to be monitored.

United Utilities is responsible for electricity distribution in the North West of England, an area of 12,000km2 containing around 2.2 million homes.

There are over 60,000km of overhead lines and underground cables as well as 32,000 unmanned substations.

This remote-control technology is used to isolate parts of the network effected by faults and restore the remaining customers back on supply in the shortest time.

Ofgem's QoS target currently requires restoration within 3min, otherwise this counts as a customer interruption (CI) and/or customer minutes lost (CML).

This is normally a manual process of mobilising engineers to drive to the network, find the fault and isolate it by manually operating the associated switchgear.

This method is no longer adequate to reach the new supply target, so a remotely controlled automated system has become essential.

Given the geographical size of the United Utilities 11/6.6kV Secondary network, there are thousands of un-manned locations, most of them remote, that only wireless technology such as GSM can handle.

GSM has the obvious benefit of being already widely used and proven in industrial applications.

GSM provides the ability to call preset numbers and send/receive text messages, making it ideal for alarm monitoring and remote diagnostics in unmanned locations.

GSM modems are commonly used to link PLCs, data loggers, security and surveillance systems or for data acquisition.

United Utilities conducted an initial trial to test GSM in the remote locations of the rural overhead network in and around Chorley and the Peak District.

The successful outcome of this trial initiated the ENIP project through which United Utilities was looking to implement remote control initially to its worst served customers.

These customers were typically in rural locations served by the overhead network across the Peak and Lakes regions, which are prone to a higher frequency of faults/interruptions.

Using the Westermo based topology, United Utilities was able to meet the target, and improved considerably the quality of supply to these clients.

The ENIP project required a considerable number of switchgear devices to be retrofitted with a Remsdaq Callisto IES RTU (remote terminal unit), Westermo GD-01 GSM modem and an actuator device (motor) that allows the unmanned operation of the switch.

Remsdaq RTU based control systems have been installed to remotely control the open/close points; these control systems are capable of tripping/closing the associated actuator but lack communications with the central control station.

The Westermo GD-01 GSM modems are used to connect the RTUs to the central control room in Manchester.

They act as both transmitter and receiver, enabling switchgear in the network to be controlled centrally.

Other than switchgear control, the Westermo modems allow "real-time" information at the control centre regarding other inputs to the RTU, for example the equipment health and the condition of both the AC and backup DC supply.

In the United Utilities system an automation master point unit (AMPU) has been established to serve all circuits currently included in the scheme and provides for future expansion.

The AMPU acts as a data concentrator, automation controller and telecontrol interface.

The control room currently uses a bank of Westermo TD-32 analogue modems to make and receive calls with the external (remote) GD-01s.

This will shortly be upgraded to an ISDN primary rate connection to allow the Scada control system to make digital V.110 connection directly to the GD-01s.

The move to V.110 connection will reduce the connection time to the GD-01 from an average of 20-30s to just 8s.

This has the net effect of increasing the capacity of the Scada system for relatively little extra cost, but more importantly no changes to the operation of the Scada software are required.

The features of the GD-01 make it ideal for the electrical substation environment.

The unit has superior EMC characteristics in terms of immunity, surge protection and fast transients.

The RS232 interface is galvanically isolated from the supply, preventing damaging earth loops, spikes and surges.

The GD-01 has an internal watchdog and a network reregistration time to continually monitor the hardware and software these features ensure that the GD-01 is always available.

The Westermo GD-01 modem is DIN-rail mounted and can easily be retrofitted or included in new builds.

It communicates with the monitoring and control equipment via its RS232 interface using either a 9-pin D-sub or a 5-pin screw connector.

The GD-01 can be used in conjunction with other GSM modems, or traditional analogue modems and ISDN adapters.

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