How to Set a Schneider Electric's Sepam S20 Relay

Updated on March 23, 2020
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The Author is a practicing electrical engineer and has executed multiple protection-coordination projects in his professional career.

The Schneider Electric Company offers the Sepam® Series S20 relay as its mainstream protection relay for most common applications such as feeder, bus bar and substation protection.

The Sepam S20 Relay
The Sepam S20 Relay
ANSI Code
Fault Name
50
Instantaneous Overcurrent / Short Circuit
51
Time Overcurrent
50N/G
Ground or Neutral Instantaneous Overcurrent / Earth Short Circuit
51N/G
Ground or Neutral Time Overcurrent / Earth Fault
46
Current Unbalance / Negative Sequence Fault
The S20 relay offers protection against 5 basic faults.

These relays can be conveniently programmed using the SFT2841 configuration utility that is available from SE's website as a freeware.

This walk-through will assist you in setting and commissioning these relays for the various types of available fault protections using the SFT2841 utility.

Note: Values used in this article for insertion as fault parameters were determined after a proper protection coordination study. In case a protection coordination study is not available for your facility, feeder protection thumb rules can be used, which I will provide in the next article.

Initial Configuration

For the initial configuration you will need to specify the following parameters:

General characteristics screen.
General characteristics screen.
Parameter
Specification
Network Frequency
50 Hz or 60 Hz
Active Group Selection
Select which group of settings should be active. Sepam gives the option to set either group A or group B or both as active elements.
Remote Setting
Specify if the protection parameters need to accessed via remote link.
Language
English may be selected
CT Rating
Select the CT secondry rating, 1 A or 5 A
Number of CTs
Select for 3CTs or 2CTs
Rated Current
CT Primary Rating
Base Current
0.4 to 1.3 x Rated Current
Integration Period
5, 10, 15, 30, 60 mn (Select the minimum i.e 5)
Residual Current
Select 3I Sum if you have standard 3 Y-conncected CTs. This parameter specifies CT connection for measurement of 0-sequnce current by the relay.
Fault Recording Trigger
Number of periods which are recorded before the fault trigger (select the maximum).
Parameters for initial configuration.

Control Matrix for Sepam S20

The control matrix controls the activation of logic outputs and display LEDs in response to specific fault functions and input signals.

A typical configuration is shown below, which activates respective LEDs in response to each of the fault triggers.

Control matrix for Sepam S20
Control matrix for Sepam S20

Setting for 50/51 Phase Overcurrent Fault

The 50/51 phase over-current fault requires the parameters listed in the table below to be entered into the SFT2841 utility.

Phase over current fault configuration screen.
Phase over current fault configuration screen.
Parameter
Specification
Element Activity
Set to 'On' for fault trigger to be activated for this type of fault.
Tripping Curve
Select the desired characterstic curve - Standard Inverse is selected in this case.
Threshold Current
This is the pick-up value of current for the fault trigger. 326 A in this case.
Delay
This is the value of time corresponding to the value of 10 x Threshold current on the tripping curve. In this case it is set at 0.3 s corresponding to a value of 10 x 326 A = 3260 A, also marked in the TCC below.
Timer Hold Curve
Select the curve for timer delay function (definite or IDMT).
Timer Hold Delay
If a 'coordination time delay' is required it can be entered here, in this case the delay function is bypassed.
Harmonic 2 Restraint
Can be checked to avoid nuisance tripping on transformer closure. If the 2nd harmonic is detected to be 17% or higher during transformer closure, relay maloperation is prevented.
Icc Current
Icc is the rated conditional short circuit current. It is the short circuit current that a circuit breaker assembly can withstand for its operating time. Since it depends on the C.B assembly, it is the same for all faults.
Parameters for 50/51 phase overcurrent fault.

The parameters entered above, for both the phase over-current and short-circuit faults will result in the TCC plot given below, when the instantaneous and inverse-definite curves are integrated.

Typical standard inverse definite-time curve for the example relay settings demonstrated. The Inverse definite part and the instantaneous parts of the curve are integrated.
Typical standard inverse definite-time curve for the example relay settings demonstrated. The Inverse definite part and the instantaneous parts of the curve are integrated.

Setting for 50/51 - 2 Phase Short-circuit Fault

The 50/51 phase short-circuit fault requires the parameters listed in the table below to be entered into the SFT2841 utility.

Phase short-circuit fault configuration screen.
Phase short-circuit fault configuration screen.
Parameter
Specifications
Tripping Curve
Select the desired characterstic curve - Definite Time is usually selected for short circuit protection.
Threshold Current
This is the pick-up value of current for the fault trigger. 6,800 A in this case.
Delay
This is the time that the relay holds after recieving a fault trigger for a short circuit fault. It is the Horizontal asymptote of the Instantaneous part of the TCC plot. In this case it is set at 0.07 s.
Timer Hold Curve
Select the curve for timer delay function (definite or IDMT).
Timer Hold Delay
If a 'coordination time delay' is required it can be entered here, in this case the delay function is bypassed.
Harmonic 2 Restraint
Can be checked to avoid nuisance tripping on transformer closure. If the 2nd harmonic is detected to be 17% or higher during transformer closure, relay maloperation is prevented.
Parameters for 50/51 - 2 phase short-circuit fault.

Setting for 50N / 51N - 1 Earth Fault

The 50N/51N earth fault requires the parameters listed in the table below to be entered into the SFT2841 utility.

Earth fault configuration screen.
Earth fault configuration screen.
Parameter
Specification
Tripping Curve
Select the desired characterstic curve - Standard Inverse is selected in this case.
Threshold Current
This is the pick-up value of current for the fault trigger. 40 A in this case.
Delay
This is the value of time corresponding to the value of 10 x Threshold current on the tripping curve. In this case it is set at 1.5 s corresponding to a value of 10 x 40 A = 400 A, also marked in the TCC below.
Timer Hold Curve
Select the curve for timer delay function (definite or IDMT).
Timer Hold Delay
If a 'coordination time delay' is required it can be entered here, in this case the delay function is bypassed.
Harmonic 2 Restraint
This can be activated to bypass the residual current when transformers are energized.
Parameters for 50N/51N earth fault.

The parameters entered above, for both the earth and earth short-circuit faults will result in the TCC plot given below, where the instantaneous and inverse-definite curves are not integrated.

Typical standard inverse definite-time curve for the example earth fault relay settings demonstrated. The inverse definite part and the instantaneous parts of the curve are not integrated.
Typical standard inverse definite-time curve for the example earth fault relay settings demonstrated. The inverse definite part and the instantaneous parts of the curve are not integrated.

Setting for 50N / 51N - 2 Earth Short-circuit Fault

The 50N/51N earth short-circuit fault requires the parameters listed in the table below to be entered into the SFT2841 utility.

Earth short-circuit fault configuration screen.
Earth short-circuit fault configuration screen.
Parameter
Specification
Tripping Curve
Select the desired characterstic curve - Definite Time is usually selected for short circuit protection.
Threshold Current
This is the pick-up value of current for the fault trigger. 85 A in this case.
Delay
This is the time that the relay holds after recieving a fault trigger for a short circuit fault. It is the Horizontal asymptote of the Instantaneous part of the TCC plot. In this case it is set at 100 ms.
Timer Hold Curve
Select the curve for timer delay function (definite or IDMT).
Timer Hold Delay
If a 'coordination time delay' is required it can be entered here, in this case the delay function is bypassed.
Harmonic 2 Restraint
This can be activated to bypass the residual current when transformers are energized.
Parameters for 50N/51N - 2 earth short-circuit fault.

Setting for 46 - Negative Sequence Fault

The 46 negative sequence fault requires the parameters listed in the table below to be entered into the SFT2841 utility.

Negative sequence/Phase unbalance fault configuration screen.
Negative sequence/Phase unbalance fault configuration screen.
Parameter
Specification
Select Curve
Select the desired characterstic curve - Definite Time is selected in this case.
Threshold Current
This is the pick-up value of current for the fault trigger.
Delay
This is the time that the relay holds after recieving a fault trigger for negetive sequence fault. In this case it is set at 300 ms.
Parameters for 46 negative sequence fault.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

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