Elektrosrbija has been using ripple control systems for tariffs, load control and light and heat control for some years. At this moment we have four RC transmitters in use – two inject an RC signal into the 110kV transmission network, one injects an RC signal into the 35kV transmission network and the last injects the RC signal into the 20kV transmission network. The carrier frequency is 2162/3 Hz and the impulse telegram is Semagyr 52 for the 110kV network, and EDF for the 35 kV and 20kV networks. Both addressed and direct receivers are in use.
Deregulation needs flexible systems for tariffs and load management. Continuous technology development gives us new solutions to improve the practical application of an RC system, which make our system user friendly and more efficient. Our commitment is to observe new trends and technologies and to conduct experiments with new types of devices, so as to ensure we obtain maximum value from our existing equipment. This led us to develop a strategy for using both the existing and new ripple control receivers (RCRs) within our network.
Classic and new application concepts
The classic concept regarding ripple control systems (RCS) is based on the assumption that the RC signal is always available, with a large amplitude – usually over 1V at the point of receiver input – for the whole consumer area. The ripple control telegram (RCT) is transmitted at the time the RCRs should perform the desired switching action.
The shortcomings of this classic RCS concept are the large investment that has to be made in transmitters and redundant equipment; overloading of transmitting channels because of the large number of telegrams; the interference of ripple control signals transmitted from adjacent transmitters; and difficult receiver reprogramming.
Modern RCRs have the following features:
- High sensitivity on amplitude of the RC signal.
- Built-in intelligence and ability for local commu- nication and remote programming with RCTs.
- Built-in real time clock and appropriate calendar program.
These features form the technical base for introducing new approaches in ripple control systems. These new approaches are based on the following:
- Using a low level RC signal, Uopi0.1%Umii, based on the high selectivity of digital filters and position control of received pulses in time domain.
- Using an RC signal that can appear in the transmission network under certain conditions, for example by switching the transmission network to bring the RC signal in the desired consumer area.
- Using the RC signal from the upper transmission network.
- Using intelligent RCRs with built-in real time clock and appropriate calendar program.
More about RCRs
Intelligent RCRs include the functions of the classic ripple control concepts, and in addition provide receiver reprogramming in local mode, as well as in remote mode using programming RCTs. Remote programming makes the RCS flexible and user friendly, because the RCRs can be reprogrammed easily and simultaneously. Local on-site reprogramming can be achieved by an optical port, according to IEC 1107, or by other interfaces.
RCS with intelligent RCRs, including a real time clock, cover the functions of both classic RCS and RCS with intelligent receivers, allowing the RCS to be operated in different modes:
- Conventional mode – reception of telegrams when output action is desired.
- Autonomous receiver operation mode, when the RC signal is missing, based on the built-in program and real time clock
- Reception of programming telegrams and reprogramming of RCRs.
The autonomous receiver operation mode provides more reliable function of RCRs when signalling conditions on the power network are difficult. It reduces the number of necessary telegrams, and does away with the problem of redundant equipment, because there is no need for the continuous presence of an RC signal.
The real time clock mode can save investment in areas when installation of RC transmitters is anticipated.
Remote programming is sometimes possible if switching of the transmission network can provide the energy flow that brings the RC signal to the desired consumer area. A mobile ripple control transmitter can also be used.
Tests and experiments
Before making a decision to start using the new concept RCS, we conducted the following experi- ments over a period of four months:
- Experiments with sensitive RCRs with a signal threshold level of 0.2V, (0.1%Um).
- Experiments with intelligent RCRs with a signal threshold level of 0.45V, (0.2%Um) and built-in real time clock and calendar program.
- Experiments with intelligent RCRs which could be programmed remotely by RCTs.
All these experiments, using the approved technical features of modern RCRs, showed a high level of reliability in use, reception and decoding of RCTs, even when the RC signal level is only 0.2V. There were no operating problems with the RCRs during the experiments. The receivers worked normally even when an RC signal was not present, under the control of a real time clock, programmed functions and/or calendar program.
Using remote programming and reprogramming by specific programming protocols and RCTs, we successfully changed the switching times in receivers, the set and cancel function of autonomous operation in receivers, achieving time synchronisation of the receivers.
In addition, it should be noted that the power network has a low level of third and fifth harmonic, and there were almost no disturbances that could influence the performance of the receivers. The selectivity curve of the RCRs used in the experiments is shown in Figure 1.
The bandwidth is 4Hz and extinction of the third and fifth harmonic is better than 60dB. Filter Q factor > 20.
In planning our use of RCRs, we divided the company's supply area into three categories, depending on the amplitude and availability of the RC signal:
Category A: Supply area with an RC signal that is always available, with sufficient amplitude.
Category B: Supply area with a large or small amplitude of the RC signal that appears periodically.
Category C: Supply area without an RC signal.
Based on these three categories and our experiments, we decided to build the following categories of RCRs:
- Category A: RCRs without built-in intelligence and with a programmed signal threshold level in the RCR over 1V. Sensitive RCRs can also be used in areas of Category A with the RC signal level 0.1%UmUoiii0.2%Um.
- Category B: RCRs with built-in intelligence, real time clock and with a programmed signal threshold level Uop=(0.2- 0.3)%Um. In these areas time synchronisation of the receivers and potential reprogramming can take place several times during the year, when the appro- priate switching condition of the transmission network can be achieved.
- Category C: RCRs with built-in intelligence, real time clock and with a programmed signal thresh- old level of Uop=0.2%Um. The main objective is to prepare the consumption area for the time when the RC transmitters will be built.
We tried to improve on the classic concept of RCS by using sensitive RCRs. They provide reliable reception and decoding of RCTs, even when the amplitude of the signal is small – 0.2V (0.1%Um). Successful and reliable reception is achieved due to the high selectivity of digital filters and position control of received pulses in time domain.
The following benefits were achieved:
- Decrease in investment in new ripple control transmitters.
- Increase of the consumption area covered with a quality RC signal.
- Maximum level of use of the existing RC transmitters.
At the same time the reliability and efficiency of the system has been maintained.