Overcurrent and Distance Protection in DigSilent PowerFactory

Electrical Engineering Specialization
Power System Protection and Protection Devices using DIgSILENT
PowerFactory
Presented By: Examiner 1:
Areeb Abdullah (217205647) Prof.Dr.-Ing.Lijun Cai
Salah Shehata (217205346) Examiner 2 :
M.Sc. Qusay Abdel Latif
17.03.2019 © 2009 UNIVERSITÄT ROSTOCK | FAKULTÄT FÜR INFORMATIK UND ELEKTROTECHNIK 1

1. Introduction
2. Literature Review
3. Functional Blocks Study
4. Procedure
5. Simulations
6. Results
7. Conclusion
Contents

• Need of protection devices in the power system.
• Theoretical study of protection devices and both protection schemes.
• Analysis of control and logical blocks of Siemens and Generic relays.
• Modelling of network followed by Load Flow and Short Circuit Analysis.
• Representation and implementation of Overcurrent Protection and Distance
Protection in DIgSILENT PowerFactory.
• Application of various faults with different protective characteristics to observe
the best possible relay coordination protection.
Introduction

Literature Review
and Functional
Blocks Study
System Modelling
in Power Factory
Load Flow and
Short Circuit
Analysis
Overcurrent/
Distance Relay
Coordination
Investigate
Results
Methodology

Fuse:
Interrupts current when current reaches the pre defined value. Its operation
involves two phases i.e. melting and current interruption.
Relay:
Protective equipment detects a fault and sends trip signal to circuit breakers.
Circuit Breaker:
Receives input from relay and opens its contact to clear a fault.
Recloser:
Limited fault interrupting capability and recloses automatically in a programmed
sequence.
Protection Devices

There are two types of instrument transformers:
i. Current Transformer.
ii. Voltage/Potential Transformer.
Instrument Transformers are used to step down the voltage and current within
range of the existing measuring instruments of moderate size.
Instrument Transformers

CTs are designed to withstand fault current
for a few seconds.
Construction Types of CT:
1. Window.
2. Bar type.
Categories of CT of standard secondary rating (IEC61869-2):
1. 1 Amp 2. 2 Amp 3. 5 Amp
CT selection criteria :
a) CT class criteria.
b) Core construction.
c) Capacity.
Current transformer (CT)
500/1A 5VA 5P 20
BurdenPri. A/Sec. A
Accuracy
Abbreviation for protection
Name Plate Identification
Highest current value
with respect to rated
value
https://goo.gl/images/e6dkNf

CT equivalent circuit
https://goo.gl/images/WvmBGR

Used in electrical power system for stepping down the system voltage to a safe value
which can be fed to low rating meters and relays.
Type of potential transformers:
1. Electromagnetic voltage transformer.
2. Capacitive voltage transformer.
Category of VT of standard secondary rating(IEC61868-3):
a) Based on the current practice of a group of European countries:
– 100 V and 110 V.
– 200 V for extended secondary circuits.
b) Based on the current practice in United States and Canada:
– 120 V for distribution systems.
– 115 V for transmission systems.
– 230 V for extended secondary circuits.
Voltage transformer (VT)

VT equivalent circuit
https://goo.gl/images/ZYMWha

Based on operating characteristics, it can be divided
into three groups:
1) Instantaneous or Definite Time.
2) Inverse Definite Minimum Time.
I. Standard Inverse
II. Very Inverse (VI)
III. Extremely Inverse
3) Directional Overcurrent Relay.
Overcurrent Protection

• Load flow and Short Circuit Analysis.
• Minimizing the overall operating time of relay.
• IEC 60255 defines a formula to simulate different time/overcurrent
characteristics of overcurrent relays.
𝑇𝑝 =
𝑐
𝐼𝑓
𝐼 𝑝
𝛼
− 1
× 𝑇𝑀𝑆
𝑇𝑝 = 𝑂𝑝𝑒𝑟𝑎𝑡𝑖𝑛𝑔 𝑡𝑖𝑚𝑒 𝑖𝑛 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 , 𝑇𝑀𝑆 = 𝑇𝑖𝑚𝑒 𝑀𝑢𝑙𝑡𝑖𝑝𝑙𝑖𝑒𝑟 𝑆𝑒𝑡𝑡𝑖𝑛𝑔𝑠
𝑐 = 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑓𝑜𝑟 𝑟𝑒𝑙𝑎𝑦 𝑐ℎ𝑎𝑟𝑎𝑐𝑡𝑒𝑟𝑖𝑠𝑖𝑡𝑐𝑠, 𝛼= 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑜𝑓 𝑅𝑒𝑙𝑎𝑦
𝐼𝑓 = 𝐹𝑎𝑢𝑙𝑡 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑣𝑎𝑙𝑢𝑒, 𝐼 𝑝 = 𝑅𝑒𝑙𝑎𝑦 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑠𝑒𝑡𝑡𝑖𝑛𝑔
Plug Setting Multiplier and Time Setting Multiplier

7SJ61 Overcurrent Relay
Control and Logical Blocks

• Set up a model using modified IEEE system.
• Load Flow and Short Circuit Analysis.
• Finding PSM and TSM using both analysis to obtain relay operating
parameters for proper coordination.
• Implementation of Siemens and Generic relays.
Procedure

Single line diagram of network model use for overcurrent protection
Simulations

Relay Types and Settings
Protection
Device
Location Model Stage Current
(pri.A)
Current
(sec.A)
Time Characteristic
Relay1 Bus 1 7SJ61_1A_1A_EF Ip51 100 1.00 0.57 IEC 255-3 Inverse
I>50_1 1171 11.71 0.38 Definite
Relay 2 Bus 2 7SJ61_1A_1A_EF Ip51 100 1.00 0.50 IEC 255-3 Inverse
I>50_1 586 5.86 0.38 Definite
I>50_1 391 3.91 0.38 Definite
I>50_1 293 2.93 0.38 Definite
Generic Bus 4 F50_F51 Phase
Overcurrent
I> 110 1.10 1.00 IEC Class B
(Very Intensive)
I>> 300 3.00 1.00 Definite

Single Phase to Ground Fault at Bus 3
Results

Three Phase Fault at Bus 5 with Generic Relay Protection

Short Circuit Sweep

1. Overcurrent protection coordination is highly constrained objective in radial
feeder distribution system.
2. Change in method for short circuit analysis for real time applications.
3. Time-Overcurrent characteristic curve influence tripping time of relay.
4. Generic protection is slow as compared to Siemens Relay.
5. Relay coordination with proper grading margin is successfully demonstrated.
6. Appropriate functionality of relay cannot be achieved in case of meshed
networks.
7. Blinding problem caused by Distributed Generators.
Conclusion

• The principle describes as when impedance of transmission line is proportional to its
length. Where,
• Implement secondary impedance because measuring values for voltage and current from
secondary side of CT and VT,
Mode of Operation:
• Due to inaccuracy in the distance measurement, practical 100% of line length is not
possible.
• Grading which is coordination between zone reach and time.
Distance protection
I
VZ 
prim
ratio
ratio
Z
VT
CT
Z sec

Siemens Distance Protection Relay (7SA6)
• Sta-Vt Block: This block represents the behavior of voltage transformer (VT).
• ElmRelay Block: This is compilation block .CT, Measurement and Logic
blocks are same as explained in overcurrent section.
Generic Distance Protection Relay (7SA6)
1. Reldisloadenc Block
2. RelFdetect Block
3. RelDisdir Block
4. RelDispoly Block
5. RelZpol Block
Control and Logical Blocks

• Operation boundaries can be determined and defined by fixed shape in R-X diagram.
• Relay operates at any values inside this shape.
• Choice of characteristics of relay depend on the application, direction option and load
impedance.
Basic Distance Relay Characteristic types:
1. Impedance
It is represented by circle with center at the origin.
Distance Relay Characteristics

It is represented by circle with its circumference passing
through origin.
2. MHO
3. Offset MHO
It is represented by circle being shifted.

.
4. Reactance
It is represented by straight line parallel to R-axis. It
provides non directional trip under load.
5. Quadrilateral
It is represented by shape with 4 sides.

.
It looks like offset mho but shaped by lens while aspect
ratio is adjustable to reduce sensitivity in high load
impedance.
6. Lenticular
7. Polygonal
It looks like quadrilateral but choice between
both depends on application.

• Set up a model using modified IEEE system and select the path.
• Load Flow and select CTs and VTs.
• Implementation of Siemens and Generic relays.
• Implement distance coordination method and tripping time.
• Studying cases.
Procedure
Simulation

Set up a model using modified IEEE system and select the path

Current and Voltage Transformer Ratio
No. Line Length(km) CT Ratio
(pri/sec)
VT Ratio
(pri/sec)
Protection
Relay
Manufacture
1 Line_009_014 40 200/1 33000/100 F21 Distance
Polygonal
DIgSILENT
2 Line_013_014 50 150/1 33000/100 F21 Distance
Polygonal
DIgSILENT
3 Line_013_016 60 400/1 33000/100 F21 Distance
Polygonal
DIgSILENT

• Independent method with zone factor (zone1=85%, zone2=40% and zone 3=20%).
• Tripping time calculated by coordination results.
Implement distance coordination method and tripping time

As expected from time distance diagram, both of relays trip
CB instantaneously
Case 1 : Three phase short circuit at line_0013_0014 at 50% of length
(Siemens relay)
Study cases (Siemens relay)

Case 2: Three phase short circuit at line_0006_0013 at 5% of length from
bus_0013.
As expected from time distance diagram one of them trip CB
instantaneously and other one back ups after time grading

Compare time distance diagram so it failed
in this study case
Study cases (Generic relay)

Thank you

Overcurrent and Distance Protection in DigSilent PowerFactory

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