Protective Relaying for DER Rogerio Scharlach Schweitzer Engineering Laboratories, Inc. Basking Ridge, NJ
Overview IEEE 1547 general requirements to be met at point of common coupling (PCC) Distributed resource (DR) response to area electric power system (EPS) abnormal conditions
Overview Distributed generation (DG) impact on distribution feeders Real Life Operation of DR Interconnection Protection Introduction to Symmetrical Components
IEEE 1547 General Requirements to Be Met at PCC Voltage regulation Integration with area EPS grounding Synchronization Inadvertent energization of area EPS Monitoring provisions Isolation devices Interconnection integrity
DR Response to Area EPS Abnormal Conditions Faults Reclosing Voltage excursions Frequency excursions Loss of synchronism Reconnection to area EPS
DR Response to Area EPS Faults DR unit shall cease to energize area EPS for faults on area EPS circuit to which it is connected
DR Response to Area EPS Reclosing DR shall cease to energize area EPS circuit to which it is connected prior to reclosing by area EPS
DR Response to Voltage Excursions Voltage parameters are to be met at PCC Interconnection system responds to rms or fundamental voltage Phase to phase Phase to neutral Voltage Range (% of base voltage) Clearing Time (s) V < 50 0.16 50 V 88 2.00 110 V 120 1.00 V 120 0.16
DR Response to Frequency Excursions DR shall cease to energize area EPS when system frequency is in particular range DR Size Frequency Range (Hz) Clearing Time (s) 30 kw > 30 kw > 60.5 0.16 < 59.3 0.16 > 60.5 0.16 < 59.8 to 57.0 (adjustable) 0.16 to 300 (adjustable) < 57.0 0.16
DR Response to Loss of Synchronism In this case, DR response Applies only to synchronous generators Is primarily a risk to generators Standard addresses this condition as being of concern only if it results in voltage fluctuations that violate flicker limitations
DR Reconnection to Area EPS Reconnection is delayed up to 5 minutes after area EPS steady-state voltage and frequency are restored Ranges include Frequency 59.3 to 60.5 Hz Voltage see ANSI C84.1-1995, Table 1
Power Quality Limitation to dc injection Limitation of flicker induced by DR Harmonics
Islanding Unintentional Intentional
DG Impact on Distribution Feeders Increased fault duty Unintentional islanding Relay desensitization Nuisance tripping Automatic reclosing Voltage regulation and flicker Ferroresonance
Increased Fault Duty Is caused by addition of generating sources and rotating machinery of considerable size Affects capability of equipment to carry and interrupt fault currents Requires both local and area EPS equipment ratings to be reevaluated
Unintentional Islanding Occurs when portion of area EPS and DR become electrically isolated from rest of area EPS and DR continues to energize island Should be avoided for two major reasons There is potential for negative effects on voltage, frequency, and power quality Islanded generator complicates both automatic reclosing and manual switching
Relay Desensitization Available short-circuit current increases with addition of DR Short-circuit current splits between substation and DR Substation short-circuit contribution can be significantly reduced when compared with value before addition of DR
Relay Desensitization Fault Current Distribution Without DR Substation 323 198 R1 R2 Three-Phase 3I 0 323 A 198 A F1
Relay Desensitization Fault Current Distribution With DR Substation 199 24 R1 R2 200 246 DR Substation Three-Phase 3I 0 199 A 24 A DR 399 Three-Phase 3I 0 270 200 A 246 A F1
Nuisance Tripping Without DR F2 Substation 762 616 R1 R2 Three-Phase 3I 0 762 A 616 A
Nuisance Tripping With DR Substation 762 616 R1 1530 616 F2 R2 768 0 DR Substation Three-Phase 3I 0 762 A 616 A DR Three-Phase 3I 0 3E 0 768 A 0 A 0.729 pu 3E 0
Operation for Fault in Adjacent Zone I SYS + I FAULT SYS 1 I SYS I FAULT 2 3 I FAULT DR
Automatic Reclosing DR should be disconnected before open interval expires By interconnection protection (81U, 81O, 59, 27) By DTT Minimum open or dead time to allow arc deionization and to avoid restrike is
Automatic Reclosing If DR can form sustainable island when separated from system, restoration becomes issue Utility feeder breaker has to be equipped with synchronism-check element and / or live-bus and dead-line logic OR combination of both elements works as permissive for reclosing utility feeder breaker
Automatic Reclosing Close Permissives Utility Bus Feeder and bus are in synchronism Utility bus is hot and line is dead DR 3 C T 3 Live Bus / Dead Line or Synchronism 1 Temporary Fault Multifunction Relay
PV Array Real Life Operation of DR Interconnection Protection Isolation Transformer 380 Vac 13,800 Vac Neutral Grounding Reactor 51P 51G Pole-mounted Recloser T C I VY VZ 81 59 59G 27 Recloser Control Overhead Distribution Feeder Ø-G Fault Simplified Single-Line Diagram
Recloser Control Simplified Trip Logic 27-1 27-2 59-1 59-2 81-1 OR 81-2 81-3 59G 51P 51G OR OR TRIP RECLOSER
Relay Settings Element Setting Delay Description 27-1 50% 108.33 ms Definite time undervoltage level 1 27-2 88% 1.950 s Definite time undervoltage level 2 59-1 110% 950 ms Definite time overvoltage level 1 59-2 120% 108.33 ms Definite time overvoltage level 2 81-1 57 Hz 78.95 ms (@ 57 Hz) Definite time underfrequency level 1 81-2 58.5 Hz 102.6 s (@ 58.5 Hz) Definite time underfrequency level 2 81-3 60.5 Hz 74.38 ms (@ 60.5 Hz) Definite time overfrequency 59G 8,200 V 1.33 s Definite time residual ground overvoltage 51P 60 A NA Inverse time phase overcurrent 51G 19.8 A NA Inverse time residual ground overcurrent
Relay Underfrequency Settings
Feeder Fault (C-Ground)
Undervoltage Element Pickup Time 15.62 ms
Undervoltage Element Time Delay 108.33 ms
Recloser Interruption Time 17.71 ms
141.66 ms Total Clearing Time
Introduction to Symmetrical Components The solution of balanced multi-phase systems can be accomplished using singlephase methods The method of symmetrical components allows unbalanced multi-phase systems to be solved using single-phase methods. Introduced in 1918 by C.L. Fortescue
Insight it is shown that unbalanced problems can be solved by the resolution of the currents and voltages into certain symmetrical relations. When the constants are symmetrical, that is, when the system viewed from any phase is similar, then the symmetrical components of currents do not react upon each other so that it becomes possible to eliminate the mutual relations with their attendant complication in the solution of the problems. C.L. Fortescue
Decomposition of an Unbalancedd System
Symmetrical Components as a Function of Phase Quantities
Phase Quantities as a Function of Symmetrical Components
Phase-to-Ground Fault Two-Terminal System
Zero Sequence Network During the Fault + - N 0 ΔV 0 = I 0R * (3 x Z N + Z 0TR ) Z 0S I 0DR = 0 Z 0DR 3 x Z N I 0S 0 V 0Z X H 0 Z 0TR ΔV 0 CB CLOSED I 0S + I 0R R CLOSED V 0Z before trip = 2400 V < 2,735 V (pick up) V 0Z after trip = 3200 V > 2,735 V (pick up) H
Residual Ground Overvoltage
Sample DER Interconnected Through PV Array a Delta/ Wye Transformer Isolation Transformer Pole-mounted Recloser T C I VY VZ Overhead Distribution Feeder Ø-G Fault 51P 81 59 27 51G 59G Recloser Control Simplified Single-Line Diagram
E What is the 3V0 at the Recloser Location After Utility Separation? Z 1S I 1S = 0 CB OPEN Z 2S I 2S = 0 CB OPEN Z 0S I 0S = 0 Z 1L Z 2L V 1 V 2 V 0 R CLOSED R CLOSED I 1DR = 0 I 2DR = 0 Z 0DR X Z 1DR Z 1TR Z 2DR Z 2TR I 0DR = 0 H 0 Z0TR H CB OPEN Z 0L R CLOSED I 0R = 0
Conclusions There are several requirements to be met by DR at PCC location DR has to respond to abnormal conditions of area EPS Addition of DR to distribution feeder affects its protection, voltage regulation, fault duty, reclosing scheme, and so on
Conclusions Event report analysis is a great tool to validate DER interconnection protection settings Unbalanced phasors can be broken down into their symmetrical components Symmetrical components allow the use of simple single-phase calculations for analysis of unbalanced systems The resultant symmetrical components can be recombined into the phase components
Questions?
Questions to the audience Please provide 3 examples of DR impacts on distribution feeders. Please provide 3 examples of area EPS abnormal conditions that the DR has to respond to. Can a DR immediately reconnect following a successful feeder restoration? If not, how long is the qualifying time delay? What are the quantities monitored during the qualifying time delay?
Questions to the audience According to the theory of Symmetrical Components, an unbalanced set of currents can be decomposed in three other components. What are these components? How are the sequence networks interconnected to represent a phase-toground fault?