Testing Non-Directional Overcurrent Protection Practical Example of Use
Testing Non-Directional Overcurrent Protection
Manual Version: Expl_OVC_NonDir.AE.1 - Year 2011 © OMICRON electronics. All rights reserved. This manual is a publication of OMICRON electronics GmbH. All rights including translation reserved. The product information, specifications, and technical data embodied in this manual represent the technical status at the time of writing and are subject to change without prior notice. We have done our best to ensure that the information given in this manual is useful, accurate, up-to-date and reliable. However, OMICRON electronics does not assume responsibility for any inaccuracies which may be present. The user is responsible for every application that makes use of an OMICRON product. OMICRON electronics translates this manual from the source language English into a number of other languages. Any translation of this manual is done for local requirements, and in the event of a dispute between the English and a non-English version, the English version of this manual shall govern.
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Preface This paper describes how to test non-directional overcurrent protection elements. It contains an application example which will be used throughout the paper. The theoretical background of the non-directional overcurrent protection will be explained. This paper also covers the definition of the necessary Test Object settings as well as the Hardware Configuration for non-directional overcurrent tests. Finally the Overcurrent test module is used to perform the tests which are needed for the non-directional overcurrent protection function. Supplements:
Sample Control Center file Example_Overcurrent_OvercurrentNonDirectional_ENU.occ (referred to in this document). Test Universe 2.40 or later; Overcurrent and Control Center licenses.
Requirements:
1
Application Example 10.5 kV Protection functions 1st element (51) / non-directional characteristic (IDMT) 200/1 2nd element (50/51) / non-directional characteristic (DTOC) Overcurrent Relay
Figure 1: Feeder connection diagram of the application example
Parameter Name
Parameter Value
Frequency
50 Hz
CT (primary/secondary)
200 A /1 A
1st element
2nd element
Notes
IEC Very Inverse
Tripping characteristic
300 A
Pick-up 1.5 x In CT primary
1.2
Time multiplier setting (TD; TMS; P, etc.) (only for IDMT characteristics)
DTOC
Tripping characteristic
600 A
Pick-up 3 x In CT primary
100 ms
Trip time delay
Table 1: Relay parameters for this example
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Theoretical Introduction to Overcurrent Characteristics
2.1
Tripping Characteristics There are two major overcurrent characteristic types: Inverse time and definite time. Tripping Characteristics
Inverse-Definite Minimum Time Overcurrent Relay
Definite Time Overcurrent Relay
Trip-time charateristic of a twoelement DTOC relay
Trip-time characteristic of an IDMT overcurrent relay
t/s
t/s
t(1st el.) t(2nd el.)
t(2nd el.)
1stelement 50-1/51 or 50N-1/51N
2ndelement I/I P 50-2 or 50N-2
1stelement
2ndelement
I/IP
51 or 51N or 67
Inverse time characteristics can have different basic shapes such as these: Characteristic
Formula
Annotation
LTI (long time inverse)
t
120 T I IP 1 P
t
0.14
SI (standard inverse)
VI (very inverse)
t
I IP 1
t
80
EI (extremely inverse)
I IP 0.02 1 13.5
Suitable for motors, for example.
TP
TP
I IP 2 1
TP
Suitable for co-ordination with fuse tripping characteristics.
Table 2: IDMT tripping characteristics (see IEC 60255-3 or BS 142, section 3.5.2)
t TP or TMS I IP Note:
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= = = =
trip time in seconds setting value of the time multiplier fault current setting value of the pick-up current
Some relays have an increased pick-up value for IDMT characteristics. For example, the relay used in this example has an actual pick-up value that is 1.1 times higher than the IP setting.
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2.2
IDMT Characteristics (51, 51N) As the properties of the operational equipment differ considerably (overload, short circuit behavior, etc.), the characteristics have to be adapted to this.
1
2
3
5 4
6 6 7
7 8
Figure 2: Parameters of an overcurrent relay (AREVA)
1. 2. 3. 4. 5. 6. 7. 8.
Tripping characteristic for the 1st element (for this example IDMT IEC very inverse) Directional function (for this example non-directional) Pick-up setting (primary) of 1st element Pick-up value at 1.1 x IP Time multiplier setting (TMS) for the 1st element Tripping characteristic for the 2nd element (DTOC for this example) Pick-up setting (primary) of 2nd element Trip time delay of 2nd element 1000
5 1 100
1
10
1
6
8 1 0.1 3 1 0.01 200
300
7 1 4 1
400
IEC Very Inverse (TMS = 1.2)
500
600
IEC Very Inverse (TMS = 4)
700
800
900
IEC Very Inverse (TMS = 6)
Figure 3: Comparison of IEC very inverse tripping characteristics with different time multiplier settings (TMS)
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Practical Introduction to Overcurrent Characteristic Testing The Overcurrent test module is designed for testing directional and non-directional overcurrent protection functions with DTOC or IDMT tripping characteristics (short-circuit, thermal overload, zero sequence, negative sequence, and customized curve characteristics). The test module can be found on the Start Page of the OMICRON Test Universe. It can also be inserted into an OCC File (Control Center document).
3.1
Defining the Test Object Before testing can begin the settings of the relay to be tested must be defined. In order to do that, the Test Object has to be opened by double clicking the Test Object in the OCC file or by clicking the Test Object button in the test module.
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3.1.1 Device Settings General relay settings (e.g., relay type, relay ID, substation details, CT and VT parameters) are entered in the RIO function Device.
Note:
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The parameters V max and I max limit the output of the currents and voltages to prevent damage to the device under test. These values must be adapted to the respective Hardware Configuration when connecting the outputs in parallel or when using an amplifier. The user should consult the manual of the device under test to make sure that its input rating will not be exceeded.
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3.1.2 Defining the Overcurrent Protection Parameters More specific data concerning the overcurrent relay can be entered in the RIO function Overcurrent. The definition of the overcurrent characteristic must also be made here.
Note:
Once an Overcurrent test module is inserted this RIO function is available.
Relay Parameters This first tab contains the definition of the directional behavior as well as the relay tolerances.
1
2 1
1. 2.
Since we want to test a non-directional overcurrent relay this option has to be chosen. The current and time tolerances can be obtained from the relay manual.
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Elements This tab defines the characteristic of the different overcurrent elements.
1 6 5 2
5 3
3 4
4
The default overcurrent characteristic is shown above. It contains an IEC Definite Time scheme with one element for a phase overcurrent protection. This characteristic has to be adjusted to the parameters of the relay (Table 1): 1.
2. 3. 4. 5.
6.
In order to define the elements of the phase overcurrent protection, select Phase as the Selected element type. Note: If other element types are also present in the relay select the related element types consecutively in (1) to enter these elements. The selection field shows the number of already defined related elements and how many of these are marked as active. This table shows the elements which define the tripping characteristic for the selected element type. The name of the first element may be changed according to the name used in the relay, e.g., "I>1". Change the characteristic type of the first element to IEC Very inverse (Table 1). Afterwards set I Pick-up and the Time index. As mentioned in chapter 2.1 , the 1st element has an increased pick-up value (by factor 1.1). This has to be considered in the Range limits of the test object. In order to do that, select Active and enter the increased pick-up value in I min.
Now the second element can be added. It has an IEC Definite Time characteristic which might be renamed to "I>2". Also set I Pick-up and the Trip time.
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The list of the elements appearing after these adjustments is shown below.
1
1.
The Reset Ratio must also be checked in the manual.
The resulting overcurrent characteristic is shown below. A 1st element B 2nd element
A B
1 A A 1 B B
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3.2
Global Hardware Configuration of the CMC Test Set The global Hardware Configuration specifies the general input/output configuration of the CMC test set. It is valid for all subsequent test modules and, therefore, it has to be defined according to the relay’s connections. It can be opened by double clicking the Hardware Configuration entry in the OCC file.
3.2.1 Example Output Configuration for Protection Relays with a Secondary Nominal Current of 1 A
IA IB IC IN
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3.2.2 Example Output Configuration for Protection Relays with a Secondary Nominal Current of 5 A
IA
IC IB
Note:
IN
Make sure that the rating of the wires is sufficient when connecting the outputs in parallel. The following explanations only apply to protection relays with a secondary nominal current of 1 A.
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3.2.3 Analog Outputs
The analog outputs, binary inputs and outputs can all be activated individually in the local Hardware Configuration of the specific test module (see chapter 3.3 ). 3.2.4 Binary Inputs 4
3
1 2
1. 2. 3.
Trip
Start
4.
The start command is optional (it is needed if Starting is selected as the time reference in the test module or if a pick-up / drop-off test is required). The trip command has to be connected to a binary input. BI1 … BI10 can be used. For wet contacts adapt the nominal voltages of the binary inputs to the voltage of the circuit breaker trip command or select Potential Free for dry contacts. The binary outputs and analog inputs etc. will not be used for the following tests.
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3.2.5 Wiring of the Test Set for Relays with a Secondary Nominal Current of 1A Note:
The following wiring diagrams are examples only. The wiring of the analog current inputs may be different if additional protective functions such as sensitive ground fault protection are provided. In this case IN may be wired separately.
Protection Relay
(-) (-)
IA IB IC IN
Trip optional
(+) Start (+)
Protection Relay
(-) (-)
IA IB IC IN
Trip optional
(+) Start (+)
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3.3
Local Hardware Configuration for Non-Directional Overcurrent Testing The local Hardware Configuration activates the outputs/inputs of the CMC test set for the selected test module. Therefore, it has to be defined for each test module separately. It can be opened by clicking the Hardware Configuration button in the test module.
3.3.1 Analog Outputs
3.3.2 Binary Inputs
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3.4
Defining the Test Configuration
3.4.1 General Approach When testing the non-directional overcurrent protection, the following steps are recommended: > Pick-up Test: Testing the pick-up value of the overcurrent protection (only if the start contact is wired for this relay, or if the relay is of the Ferraris disk type – see Help for more information). > Trip time characteristic: Verifying the trip times of every element of the tripping characteristic. Each of these tests can be performed with the Overcurrent test module.
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3.4.2 Pick-Up Test 2
1
3
4
1.
2. 3. 4.
5
6
For this test, it is not necessary to define a trigger in the Trigger tab. The pick-up test can be performed if a start contact is wired and defined as a test module input signal in the local Hardware Configuration (see chapter 3.3 ). Settings in the Fault tab will not be needed in this test (but might be added to combine pick-up and characteristic tests in one module). As the start contact is used to trigger this test, Relay with start contact has to be chosen. The phase overcurrent function is tested with phase to phase faults. Note: In this case other protection functions may interfere with the test. However, if such functions or elements (e.g., ground fault protection, negative sequence protection, etc.) are present they may be specified in the Test Object in the same manner as the phase elements were entered in this example. The resulting characteristic will be calculated individually and shown for each test shot depending on its fault type (4) and fault angle (5), ensuring a proper assessment according to the expected overall relay behavior.
5. 6.
For the non-directional test, no voltages are used, therefore, no test angle can be set. As the pick-up is not delayed, a step length (Resolution) of 50 ms should be sufficient.
Note:
The pick-up value will be measured and assessed automatically. The drop-off value will also be measured, but it will not be assessed. The assessment of the drop-off value and of the reset ratio has to be made manually.
More test lines can be added if needed, e.g., different fault types.
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3.4.3 Trip Time Characteristic Test Trigger and Fault tabs:
2
1
1. 2. 3.
3
The trigger for this test will be the trip contact. A Load current during the pre-fault state will not be used in this example. The Absolute max. time has to be adjusted. On the one hand, it has to exceed the upper tolerance of the test point with the longest trip time otherwise an assessment will not be possible. On the other hand, it should not be set to an unnecessarily high value. For shots where No trip is expected this will be the waiting time until the assessment 'no trip' is made before continuing with the next shot. So if this time is set to a very high value, it would unnecessarily prolong the test duration.
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Characteristic Test tab:
1
2 3 4
5
1.
As the function to test is a phase overcurrent function, a phase to phase fault is used. Note: In this case other protection functions may interfere with the test. However, if such functions or elements (e.g., ground fault protection, negative sequence protection, etc.) are present they may be specified in the Test Object in the same manner as the phase elements were entered in this example. The resulting characteristic will be calculated individually and shown for each test shot depending on its fault type (1) and fault angle (2), ensuring a proper assessment according to the expected overall relay behavior.
2. 3. 4. 5.
The Angle cannot be set because no voltages are used. As the trip time of the IDMT element depends on the current, this element has to be verified with more than one test point. The trip time of the 2nd element can be confirmed with only one test point. The value of the 2nd element is also confirmed by placing two test points outside of the tolerance band of this setting. Instead of directly entering the magnitude value it can be expressed by its relation to an element setting, e.g., set Relative to: to the 2nd element and set the Factor to 1.06 (i.e., 6 % above the threshold) or 0.94 (i.e., 6 % below the threshold).
Feedback regarding this application is welcome by email at
[email protected].
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