GB2348553A - Network monitoring system - Google Patents

Abstract

A system for monitoring a distribution network has a plurality of remote transmitters each of which normally sends a low frequency narrow bandwidth signal to a central receiver over the network power lines at a characteristic frequency. When a line fault occurs, the receiver detects loss of one or more signals and is able to deduce the location of the fault.

Description

Network Alertness System The Network Alertness System (NAS) is designed to improve the reporting, location, and identification of faults anywhere on the MV or LV system and therefore minimize the fault restoration times across the entire network.

Under'normal'singie fault conditions the customer is the primary, and perhaps only, source of information to the utlity. This information is then manual collated to give a probable location for the fault on the network.

The inconsistency of this system can give poor information to the engineer and repair crews and leaves much room for mprovement However, to date, the cost and complexity of installing an automated monitoring system has been prohibitive.

1 One of the major disadvantages of the manual rnethod is the fact that the engineers are required to make assumptions based on the ~ customer information available to them. This will tend to locate the fault at the highest upstream point on any line. On average these assumptions may prove adequate but if there is more than one fault on the circuit they begin to break down.

During severe storm conditions there can be extensive damage to both the MV back-bone distribution network and the LV system. In this case the restoration of the backbone may not restore power to nearly as many customers as normal. To make matter worse, customers will not report when their supply is resumed and those which have not had their power restored usually do not think to report again that they are stiil off supply. Therefore the true extent of the network disruption can go unreported. unrecognized, and unfortunately unrepaired for a longer period than necessary.

The Keiman NAS system described here can update the utility in a matter of minutes as to the true state of the network after each fault repair and restoraton and therefore assisted immeasurably in the management of the fjeld resources available.

Automatic Fault Monitoring.

There are several requirements for a successful a systemwide system supply monitor.

It must be able to be placed in strategic locations along the MV and LV system to give a comprehensive picture of the network in real-time.

It must use a robust communication channel.

It must be fail-safe.

It must be affordable in both equipment purchase and instailation costs. it must require the minimum of -manpower for supervision on a routine basis.

It must be useful in both the urban and rural distribution network. ft must give an improvement in customer service under both normal single fault conditions and catastrophic system failure. fut must give accurate information to allow the men on the ground to be directed to the fault locations in order of system priority. fut must be capable of providing data to a central location and to other locations in the field.

As an additional benefit Quality of Supply information such as max min, and average voltage, number of supply 'dips'etc, should be provided with no additionai cost or complexity. information Channel.

The key to any effective system alertness monitor is the communication medium for the information. Although we now have the luxury of several reliable communications media there are none with the necessary coverage, especially in the more remote regions of the network..... perhaps where the system is needed most ! Even more important there are no conventional media which can satisfy the lafl-safe criterion at an economically viable cost. cost The only viable solution is to use the power lines themselves.

Power line carrier communication is not a new idea, its advantages and disadvantages are well known and it has been used successfully for a number of years. However, conventional PLC does not seem to be a promising candidate for this application because of the well documented range, power, noise, and bandwidth limitations.' The breakthrough has been to reverse the conventional wisdom of ever increasing bandwidth to communicate greater amounts of data and instead to use an ultra narrow bandwidth signal to communicate a very simple bit of information. Ultra narrow bandwidth (UNB) communications has the advantage that as the bandwidth of the signal is reduced the necessary transmission power is also reduced.

Reduced power means reduced size and cost The trade-off for this is that the data rate is also reduced, however in this application we only need to transmit single bit information and transmission times of up to 5 minutes will not present any significant problem.

The information is carried on a low power, low frequency current signal superimposed on the system load current and can easily propagate up through one or two voltage levels.

Communications A typical distribution line carrier system would use a polling architecture in which a central station sends out a packet of data and each remote station responds in tum. The NAS system differs in several ways.

Mulff-channel communicaffons.

The narrow bandwidth and low power means that many transmitters can operate simultaneously. Coding schemes that can make use of the many available channels compensate for the slow speed.

One way transmission.

Each remote transmitter operates continuously on its own frequency. This means that no central polling transmitter is needed, just a central recenser. The remote stations need no receiver or polling logic, just a transmitter.

'information Transmission.

The vital information is simply that each remote station continues to transmit If there is a fault on either the MV or LV system the transmitters which go off-line automatically give the extent of the outage. What is more, as the up-stream faults are repaired any remaining downstream faults will still be off-line until the individual faults are identifie and repaired.

The system is fail-safe in that if the remote stations malfunction they are automatically recognized as faulty, similarly if the line is damaged the signals downstream of the fault will stop transmitting.

Signal Propagation.

Since the power requirements of each transmitter is low we can use low cost coupling methods and low frequency carriers that previously were not considered practical. These signals propagate well through the distribution system, can go through transformers, are unaffected by capacitor banks, and are not subject to the standing waves or dead spots that most PLC systems experience.

Range The limiting factor on signal range is the signal to noise ratio. Field tests have shown that ranges of up to 100 miles are possible. In general the signal can propagate through most transformers of less than 10MVA rating.

Response Time.

The NAS system is capable of recognizing and reporting an outage or restoration in 5 minutes.

System Architecture.

The diagram shows a typical monitoring system for an t 1kV diution line and its associated LV circuits. The remote transmitters are connected to the LV supply at strategic points along the nework.

Installation Remote Transmitter Each remote transmitter can be installed by simple direct connection to the LV supply at the monitoring point They can be mounted in indoor or outdoor locations and because they connect to the LV supply no special tools or procedures are required. Since they can be extemaily mounted and require no phone connection the problems associated with gaining access to customer premises and interfacing to telecoms providers are eliminated.

Substation Receiver The substation receiver is connected to the system via clip-on cts around the existing protection or metering cts on the 33kV side of the transformer. It also requires no invasive installation procedures and therefore can be quickly and easiiy installe in most substations.

Each receiver is capable of monitoring over 1, 000 remote transmitters simultaneously.

Link to Network Control Centre.

Automatic Operation.

The data from each remote monitoring point is gathered at the 33 : 11kV substation source for each individual feeder. This receiver is connected to the LV suppiy in the sub and constantly monitors the incoming signals recognizing when any remote transmitter is lost In order to cope with the loss of the incoming feeder, each station receiver is equipped with a UPS to provide up to 60 minutes of operation under loss of supply conditions. Any change of system status is then reported to the Control Centre using a conventional dial-up modem, or an SMS message transmitted over the GSM network, as local conditions permit After an outage the substation receiver wil also recognize remote transmitters as they come back on-line and report the supply restoration to the Control Centre.

Manual Interrogation.

9 is also possible for the Control Centre to poll individual substations under operator control in order to confirm functionality or update the system status on a routine basis.

Equipment Requirements.

A receiver is needed at each distribution substation which may have 3 or 4 outgoing lines. We have estimated that a typical line may require around 30 remote transmitters to give coverage of the main line and HV spurs.

However the exact configuration vriil vary from system to system.

Claims (1)

1. Network Awareness System Claims Automatical reports the connection status of low voltage and medium voltage to a central control.

   Reports a !) points simultaneously.

   The transmitters are connected at low voltage and communicate up through the transformers without any additional coupling across the transformers.

   Status reports of 10, 000 points within 10 minutes.

   Reports the voltage history of the distributed points.

   Information is carried on a low power, low frequency current signal which is superimposed on the system load current