Discrimination of protection devices on installations

1. Discrimination of protection devices on installations Janet Roadway Product Manager, Power Breakers

2. Topics of Discussion • Explaining the terminology • Degrees of discrimination • Different techniques to achieve discrimination • Backup protection • Protection devices • Any Questions?

3. Protection - Basics Lets go back to basics……… • Question: Why do we use protection devices???? • Common Ans: To prevent Faults Wrong! Protection whether by fuse, circuit breaker or relay cannot prevent faults from happening. Only good design, high quality components, careful installation, preventative maintenance along with good working practices can prevent major faults However, protection devices can limit the damage and inconvenience caused if faults occur.

4. Protection - Overload • What do we mean by a fault? Overload Operating condition in an electrically undamaged circuit which causes an current to flow in excess of the full load current Example: Starting condition during DOL start If this type of fault continues indefinitely because of an anomolous operating condition., damage begins to occur creating……….

5. Protection – Short Circuit • What do we mean by a fault? Short Circuit Operating condition in an electrically damaged circuit where there is an accidental or intentional connection by a relatively low resistance between two points of a circuit which are normally at different voltages This type of fault can generate high current flows, arcing and fire if not cleared quickly

6. Discrimination Coordinate devices to: • Guarantee safety for people and installations • Identify and exclude only the zone affected by a problem • Limiting the effects of a malfunction • Reducing the stress on components in the affected zone • Ensuring service continuity with good quality supply voltage • Achieving a valid compromise between reliability, simplicity and cost effectiveness

7. Explaining the terminology • Discrimination or Selectivity • To make it possible to isolate a part of an installation involved in a fault condition from the overall system such that only the device located immediately on the supply side of the fault intervenes

8. WAIT! GO! CONTINUITY OF SERVICE FAULT DAMAGE FAULT Discrimination Needs • Fast Fault Detection • Fast Fault Elimination • Let-Through Energy Reduction • High Fault Current Withstanding

9. X A Fault occurs here X X C B Explaining the terminology

10. Degrees of discrimination • Total Discrimination • This means that the isolation described occurs for all fault levels possible at each point of the circuit

11. Degrees of discrimination t A B Prospective Fault Current Icc I

12. Degrees of discrimination • Partial Discrimination • This means that above certain current levels there is simultaneous operation of more than one protection device

13. Degrees of discrimination t A B Prospective Fault Current Icc I

14. Discrimination Traditional solutions • Current discrimination • Time discrimination • Energy discrimination • Zone (logical) discrimination

15. Discrimination Current discrimination • Discrimination among devices with different trip threshold setting in order to avoid overlapping areas. • Setting different device trip thresholds for different hierarchical levels.

16. Discrimination Current discrimination • An example:

17. Discrimination Current discrimination • Applications: • final distribution network with low rated current and low short-circuit current • ACB chains • Fault area: short circuit and overload • Discrimination limit current: low • Discrimination levels: low • Devices: ACBs, MCCBs and devices with time/current curves (contactors with thermal relays, fuses …) • Feasibility & discrimination study: easy • Customer cost: low

18. Discrimination Time discrimination • Discrimination among devices with different trip time settings in order to avoid overlapping areas • Setting different device trip delays for different hierarchical levels

19. Discrimination Electronic release L (Long delay) S (Short delay) I (IST) Setting: 0.9 Curve: B Setting: 1 Curve: A Setting: 1 Curve: A Setting: 8 Curve: D Setting: 10 Curve: C Time discrimination • An example: E4S 4000 PR111-LSI R4000 E3N 2500 PR111-LSI R2500 S7H 1600 PR211-LSI R1600 Off Off Setting: 10

20. Discrimination Time discrimination • Applications: low complexity plant • Fault area: short circuit and overload • Discrimination limit current: low, depending on the Icw of the upstream device • Discrimination levels: low, depending on the network • Devices: ACBs, MCCBs and devices with adjustable time curves • Feasibility & discrimination study: easy • Customer cost: medium

21. Types of Discrimination • Energy Discrimination • Many Low Voltage protection devices such as Circuit breakers and Fuses have the ability to limit the peak of the current let through them to a value lower than the prospective short circuit peak. • Any protective device which clears short circuits in less than 1/2 cycle of the sinusoidal wave (i.e 10mS for 50Hz) will current limit to a certain degree • Energy based discrimination is the only way to determine true discrimination between current-limiting devices

22. Discrimination Energy discrimination • Discrimination among devices with different mechanical and electrical behaviour depending on energy level • It is necessary to verify that the let-through energy of the circuit-breaker upstream is lower than the energy value needed to complete the opening of the CB downstream

23. Energy discrimination up to 24 kA Discrimination Energy discrimination • An example: Time-currents Curve

24. Discrimination Energy discrimination • Applications: medium complexity networks • Fault area: Short circuit only • Discrimination limit current: medium/high • Discrimination levels: medium, CBs’ size dependent • Devices: ACBs, MCCBs, MCBs & Fuses • Feasibility & discrimination study: medium complexity • Customer cost: medium

25. Discrimination Zone discrimination • Discrimination among devices in order to isolate the fault zone keeping unchanged feeding conditions of maximum number of devices • Zone discrimination is implemented by means of an electrical interlock between devices Zone 1 Zone 2 Zone 3

26. Discrimination Zone discrimination • Applications: high complexity plant • Fault area: short circuit, overload, ground fault • Discrimination limit current: medium, depending on Icw • Discrimination levels: high • Devices: ACBs, MCCBs with dialogue and control features • Feasibility & discrimination study: complex • Customer cost: high

27. Explaining the terminology Cascading or Backup protection • Uses supply circuit breakers or fuses with current limitation effects to protect downstream devices from damage • The amount of energy let through (i2t) by the supply device needs to be lower than that which can be withstood without damage by the device on the load side • By using this effect it is possible to install devices downstream that have short circuit breaking capacities lower than the prospective short circuit current

28. Back-up protection/Cascading • Back-up protection or Cascading is recognised and permitted by the 16th Edition of the IEE Wiring Regulations 434-03-01 and is covered by IEC 364-4-437 standard

29. Why Use Back-up Protection? • Substantial savings can be made on downstream switchgear and enclosures by using lower short circuit ratings • Substantial reductions in switchgear volumes can also result

30. What about Discrimination? • Backup protection should not be confused with discrimination. • Backup protection does not infer discrimination can be achieved but in practice, discrimination is normally achieved up to the maximum breaking capacity of the downstream device BACKUP Discrimination WAIT! GO! CONTINUITY OF SERVICE FAULT DAMAGE FAULT

31. Practical Example • Problem: Installation requires the use of Busbar rather than cable to distribute electrical power. Fault level calculations reveal 25kA prospective fault level at the point of installation of standard MCB distribution board

32. Practical Example • Solution - • Using a standard Isolator as the distribution board incoming device - all the MCBs would need to be 25kA or above • Using an MCCB as the incoming device such as an ABB Tmax T3N250TMD100, 6kA S200 MCBs could be safely used

33. A word of caution …... • Back-up protection can only be checked by laboratory tests and so only device combinations specified by the manufacturer can be guaranteed to provide co-ordination of this type.

34. Types of protection available • Fuses • Miniature Circuit Breakers • Moulded Case Circuit breakers • Air Circuit breakers

35. Typical fuse Current (A) • Ultra Reliable • Standard Characteristic • High current limitation effects • High threshold on low overloads ( clears overloads at approx 1.45x rated FLC) Time (s)

36. Fuseless technology • Two main types:- • Thermomagnetic protection- MCB and lower rated MCCB plus older type protection relays • Electronic protection – Microprocessor based relays fed from CTs either external to switches or integral within a circuit breaker

37. Thermomagnetic Time (s) Current (A) • Offer thermal longtime overcurrent protection using Bi-metal technology ( operates at 1.3x FLC) • Uses the magnetic effect of short circuit currents to offer shorttime short circuit protection Thermal curve Magnetic curve

38. Electronic Relays Time (s) Current (A) • Overcurrent functions such as:- • Long time overcurrent • Short time instantaneous protection • Short time time delayed protection • Ground fault or Earth fault protection

39. Electronic Relays Time (s) Current (A) • Overcurrent functions such as:- • Long time overcurrent • Short time instantaneous protection • Short time time delayed protection • Ground fault or Earth fault protection

40. Complete set of standard protection functions D V A Rc Hz U RV • Complete set of advanced protection functions W OT UV OV RP E  • Complete set of measurements functions VA THD VAR MORE MORE MORE Protection releases: general features

41. BACK Data logger:a professional built-in fault recorder. Data logger: a professional built-in fault recorder. • Standard in PR122 and PR123 • Recording of 8 measurements (currents and voltages); • Configurable trigger (i.e. During a fault); • Sampling frequency up to 4.800kHz; • Sampling time up to 27s; • Output data through SD-Pocket or TestBus2. Exclusive from ABB SACE.

42. Conclusion • So what is the secret to achieving a successful discrimination study • The secret is to be aware of the capability of the technology you are using and to design your installation within the limits of the protection you have chosen

44. MORE BACK MORE MORE Protectionreleases: news on standard protection functions • Double S* • Used to obtain discrimination in “critical” conditions • Double G* • Two different protection curves, one with the signal coming from internal CTs and the other from an external toroid • Dual Setting* • Two different set of protection parameters in order to protect in the best way, two different network configurations (e.g. normal supply and emergency supply) * = These features are available on PR123/P

45. Protection releases: news on standard protection functions • Double S • “low” setting on S protection function due to the settings on MV circuit-breaker • The circuit-breaker on LV side of the LV-LV trafo needs “high” settings due to the inrush current

46. Protection releases: news on standard protection functions Without double S

47. BACK Protection releases: news on standard protection functions With double S

48. MV LV Restricted Earth Fault Protection releases: news on standard protection functions • Double G • It’s possible to protect the network, with the same protection release, against earth fault both upstream and downstream the circuit-breaker • Restricted Earth Fault: the fault is upstream the LV circuit-breaker

49. MV LV Unrestricted Earth Fault Protection releases: news on standard protection functions • Double G • It’s possible to protect the network, with the same protection release, against earth fault both upstream and downstream the circuit-breaker • Restricted Earth Fault: the fault is upstream the LV circuit-breaker • Unrestricted Earth Fault: the fault is downstream the LV circuit-breaker

50. L1 Emax internal CTs Trafo secondary windings L2 L3 N External toroid PE Protection releases: news on standard protection functions • Double G • The combination of both Unrestricted and Restricted Earth Fault protection is named “Source Ground Return”. The new PR123/P is able to detect and to discriminate both earth faults • If the fault is downstream the LV circuit-breaker the PR123/P will trip Emax circuit-breaker