In the environment of high-voltage substations, protection against the serious consequences of faults is necessary if the grid is to operate safely and reliably, writes David Chamley. As power networks become larger and bus voltages increased, the focus on the design of high-voltage substations to improve their protection becomes paramount. With ancillary stations and infrastructure becoming valuable assets worth protecting, modern solutions with increased functionality are called for.
More and more, high-voltage installations are at risk of suffering damage during faults which do not lie within the protected domain of the equipment. Closely wrapped in its isolation may be the danger of cascading failures brought on through no fault of the substation’s design and is certainly not preventing a scintillation display of arcing and sparking.
Developing modern designs of sophisticated and closely monitored installations, designers are pushing the need for additional protection solutions not only to enhance safety, but to ensure maximum uninterrupted supply of grid power for the gazillions of humans who depend on it every day of their lives.Operation Interruption: Once so much power is lost, entire cities, factories and homes are left without electricity, resulting in huge sums lost overall.
Security Problem: High-voltage electricity is a danger to life, so we try to set up all possible protection systems to prevent accidents and keep our workers safe.
Main Protection Devices in a Substation of Today
Customarily, the most important protection device in a substation of high voltage is the circuit breaker. This is set to cut off or open the circuit for certain conditions of electrical failure, such as overloads or short circuits.
Gas-insulated Circuit Breakers, “GCB”: This type uses a marsh of SF6 gas to quench the electrical arc when it is forced to. It is compact and able to function efficiently under high voltages without constant attention and maintenance. Probably better than the vacuum circuit breaker, as they do not pollute because they have no SF6 in the air.
Vacuum Circuit breaker: This only uses vacuum as its interrupting medium. It has an advantage in that it requires less maintenance and presents no threat to the environment with SF6 gases.
Current Transformer and Voltage Transformer: These are just what their names imply. All this information is fed to the protection relays, where the computer will identify faults and call for breaker operation.Mainly, in substations, they continuously monitor electrical parameters (current, voltage, frequency etc). When they go out of predetermined ranges, the relay trips the circuit breaker which shuts down the defeated section of the system. Modern protection relays are highly sophisticated, have digital communications, enabling remote monitoring and control.
Distance relays: Used for sectioning faults of lines. Based on measurement of impedance between fault and relay. used where a fault appears in a HV substation and needs speedy cutting out from remainder of grid. Distinction is made between “definite time” type and inverse time which takes different lengths of time depending on intensity of disturbance and amount outside normal parameters.
Overcurrent relays: These relays serve to protect equipment from excessive flow of current. If this exceeds a certain limit it sends a signal to trip breaker.
Surge Arresters
Protect the equipment against lightning induced overvoltages (transients) and those due to switching operations by diverting surge energy to earth, hence avoiding electrical destortion to insulation or breakdown of equipment. These are designed to work in HV environments. Protecting the substation against overvoltages coming from outside.
Transformers with Built-in Protection
These are high voltage transformers with built-in temperature sensors, pressure release valves, and oil level sensors etc. Shut down automatically if something goes wrong.A sudden increase in temperature or pressure in a transformer, for example, may be a sign of an impending fault and the protection mechanism will activate to prevent possible damage.
Digital protection systems
The advent of digital technology has changed the face of all major protection systems in high-voltage substations. Digital protection systems carry with them a range of advantages over traditional electromechanical relays, including:
Faster Response Times: Digital relays can process data and respond to faults much faster than analog systems.
Remote Monitoring: With digital protection systems operators monitoring substation performance in real-time from remote locations means faster responses to a fault as well as predictive maintenance capabilities.
Data Logging: Improved digital systems can also be used to collect useful operational data to get answers to questions such as “What have been the fault trends?” and “What should be the best maintenance strategy?”.
Key Challenges and Solutions
Depreciation is not the only challenge facing those responsible for the protection of HV substations. Other challenges include the following, with ways of meeting them:
Coordination of Protection Devices. In a big HV substation, with its many associated protection devices, the danger is that during a fault, the wrong sections of the network might be switched off. For this reason, coordination of the protection devices is critical. For example, make use of selective coordination. This is where the closest breaker to the fault is the only breaker switched off (tripped), the plan being to maintain as many other sections of the larger network as possible in service.
Cybersecurity Risks. As substations become digitally integrated to a greater extent so the risk of their becoming subjected to external cyberattack rises; therefore, good cyber protection of all devices is called for. Network security measures such as firewalls, encryption, and intrusion detection are needed in order to help stop outside access to protection systems.
System Overload. Overloading of the connected equipment of the big HV substation could occur for several reasons – around the failure of equipment, for instance, and because of large increases and decreases in demand. Use of proper protection routinely will detect such overload conditions and prevent damage to the system in any situation.
Protection System Maintenance. Testing and indeed general maintenance of the devices and ideally all parts of the system is essential, of course, if it is to prove reliable in the event of a genuine fault condition. Scheduling suitable inspections and tests of protective relays and also verifying correct tripping of circuit breakers is appropriate.
Conclusion
Protection of high-voltage substations is crucial for the reliability and safety of the electrical network. As they change and progress, the need for advanced protection systems becomes clearer, and all major operational protection system elements are now available; modern circuit breakers, protection relays, digital systems, and surge arresters are examples of products claimed to make for safe efficient, and reliable substation operation. Again, with the advent of more renewable generation technologies emerging and ever increasingly complex power flows, appropriate protection solutions will be demanded for maintaining electrical infrastructure reliability and longevity.