Relay testing.............................
- 2. • The testing of protection equipment may be divided into four stages: i. type tests ii. routine factory production tests iii. commissioning tests iv. periodic maintenance tests
- 3. Type Tests • Type tests are required to prove that a relay meets the published specification and complies with all relevant standards. • Comprehensive type tests simulating the operational conditions are therefore conducted at the manufacturer's works during the development and certification of the equipment. • Type testing of a digital or numerical relay involves testing of software as well as hardware, the type testing process is very complicated and more involved than a static or electromechanical relay.
- 4. Routine Factory Production Tests • Conducted to prove that relays are free from defects during manufacture. • Testing will take place at several stages during manufacture, to ensure problems are discovered at the earliest possible time and hence minimise remedial work.
- 7. Functional Tests( Type test) • Applying the appropriate inputs to the relay under test and measuring the performance to determine if it meets the specification. • They are usually carried out under controlled environmental conditions. The testing may be extensive, even where only a simple relay function is being tested.
- 8. Rating Tests(Type test) • Conducted to ensure that components are used within their specified ratings and that there are no fire or electric shock hazards under a normal load or fault condition of the power system. Thermal Withstand • Thermal withstand of VT’s, CT’s and output contact circuits is determined to ensure compliance with the specified continuous and short-term overload conditions. • Thermal withstand is assessed over a time period of 1s for CT’s and 10s for VT’s. Relay Burden • The burdens of the auxiliary supply, optically isolated inputs, VT’s and CT’s are measured to check that the product complies with its specification. • Burden increases according to the number of optically isolated input and output contact ports which are energized under normal power system load conditions. • Normally not more than 50% of such ports will be energized in any application.
- 9. Relay Inputs Inputs for auxiliary voltage, VT, CT, frequency, optically isolated digital inputs and communication circuits are tested over specified range. Relay Output Contacts Particular withstand and endurance type tests have to be carried out using d.c., since the normal supply is via a station battery. Insulation Resistance • Tested by applying 500V d.c. ±10%, for a minimum of 5 seconds. • Carried out between all circuits and case earth, between all independent circuits and across normally open contacts. • Acceptance criterion for a product in new condition is a minimum of 100MOhms.
- 10. Auxiliary Supplies • The auxiliary supply can be either a.c. or d.c., supplied from a number of sources. • Supplies - i.e. batteries, UPS’, generators, etc., may be subject to voltage dips, short interruptions and voltage variations. • The duration of the interruptions and supply dips range from 2ms to 60s intervals. • A short supply interruption or dip up to 20ms, possibly longer, should not cause any malfunction of the relay. • The relay is subjected to a number of repetitive starts or a sequence of supply interruptions. D.C Interrupt Test •Test to determine the maximum length of time that the relay can withstand an interruption in the auxiliary supply without de-energising, e.g. switching off, and that when this time is exceeded and it does transiently switch off, that no maloperation occurs. •For interruptions lasting up to and including 20ms, the relay must not de-energise or maloperate, while for longer interruptions it must not mal operate.
- 11. A.C. Ripple on D.C. Supply Determines that the relay is able to operate correctly with a superimposed a.c. voltage on the d.c. supply D.C. Ramp Down/Ramp Up This test simulates a failed station battery charger, which would result in the auxiliary voltage to the relay slowly ramping down. The ramp up part simulates the battery being recharged after discharging. The relay must power up cleanly when the voltage is applied and not maloperate. Electrostatic Discharge Test This test simulates the type of high voltage interference that occurs when an operator touches the relay’s front panel after being charged to a high potential. Enclosure Protection Test Tests prove that the casing system and connectors on the product protect against the ingress of dust, moisture, water droplets
- 12. Dielectric Voltage Withstand •Carried out as a routine test i.e. on every unit prior to dispatch. •2.0kV r.m.s., 50 Hz for 1 minute between all terminals and case earth •1.5kV r.m.s., 50/60Hz for 1 minute across normally open contacts intended for connection to tripping circuits •1.0kV r.m.s., 50/60Hz for 1 minute across the normally open contacts of watchdog output relays Insulation Withstand for Surge Overvoltages •To ensure that circuits and their components will withstand overvoltages on the power system caused by lightning. •Three positive and three negative high voltage impulses, 5kV peak, are applied between all circuits and the case earth but not across normally open contacts. Temperature Test •To ensure that a product can withstand extremes in temperatures, both hot and cold, during transit, storage and operating conditions. •Storage and transit conditions are defined as a temperature range of –25°C to +70°C and operating as –25°C to +55°C.