Relay Setting for 7ut51 Differential Protection Relay

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 1 of 12

Relay Settings for the 7UT51 Differential Protection Relay 1.0

Introduction .......................................................................................................... 1

2.0

7UT51 Relay Configuration and Settings ............................................................. 1

Application Example.................................................................................................... 2 2.1 Relay Configuration.............................................................................................. 3 2.2 Insert Transformer Data ....................................................................................... 4 2.3 Setting the Differential Function (87) .................................................................... 5 2.4 Setting the Overcurrent Protection (50HS and 50/51) .......................................... 8 2.5 Setting Output Contacts and Targets ................................................................... 9 3.0

Conclusion ......................................................................................................... 10

4.0

References ........................................................................................................ 12

1.0

Introduction

The following paper is a discussion on the setting of the 7UT512/3 Differential Relay, and consists of a simple example and various hints on how to implement settings on the 7UT512 relay. The 7UT512 require all its settings in per unit values, all rated to the nominal current of the transformer. This requires conversion for any settings performed in primary or secondary values. All the relay setting are explained in detail in the relay instruction manual but this paper can be used as a supplement to assist in the interpretation of the relay settings. To simplify the settings process, this paper will only discuss the setting of the Differential (87) and Over Current (50/51) functions.

2.0

7UT51 Relay Configuration and Settings

Follow the order of the actions below to ensure that the relay is setup up correctly and in the least amount of time. 1. Configuration of the relay for an application. 2. Insert the transformer data. 3. Setting the differential protection (87& 87HS). 4. Setting the overcurrent protection (50HS & 50/51) 5. Marshalling of the settings to output contacts and targets.

Siemens Power Transmission & Distribution Inc. Distribution Automation Division P.O. Box 29503 ! Raleigh, NC 27626-0503 Tel: (800) 347-6659 ! Fax: (919) 365-2552 ! [email protected]

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 2 of 12

Application Example Figure 1 depicts an example that will be used to implement the settings to be applied to the 7UT512. For transformer protection, the differential protection (87) must be set to 20% of nominal current of the transformer, and the instantaneous overcurrent protection (50HS) must be set to trip at 4000A in 50ms. To protect against high load currents and through faults, the inverse time element (51) must remove the transformer from the network in 10 seconds for a current of 800A. The actual settings for both the 50HS and the 51 elements are entered in per unit values, rated to the nominal current of the transformer, not in CT secondary values. The application requires that the transformer protection (the 87 and 50HS) trips the HV and LV breakers, while the transformer load protection trips only the LV breaker.`

Siemens Power Transmission & Distribution Inc. Distribution Automation Division P.O. Box 29503 ! Raleigh, NC 27626-0503 Tel: (800) 347-6659 ! Fax: (919) 365-2552 ! [email protected]

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 3 of 12

I HV sec. 600 / 5 7UT512 W1

I HV prim.

50/51

9.4 MVA 13.8 kV / 2.4 kV Z=6%

87

W2

I LV prim. 3000 / 5

I HV sec.

Figure 1: Transformer Application Example

2.1

Relay Configuration

The relay must first be configured to the application example. The example below shows the Device Options, address group 7800, under the configuration of the 7UT512 relay. The best method to understand these device options is to open a relay file in the DIGSI software and configure the relay for the intended application. This paper will not discuss the other settings under the configuration heading (7100, 7200 & 7400) . The settings contained in these address groups can normally be applied in their default state and are set during the commissioning period to set up the relay communications and fault recording options. By configuring the relay first, all protection functions that are set to be nonexistent will not appear if the setting and marshalling menus. Configuration 7800 DEVICE OPTIONS 7801 Selection of the protected object 7816 87-State of the differential protection 7821 Backup overcurrent protection

2-winding trans EXISTENT Reference side 1

s 7824 7825 7830 7831 7885 7899

49-Thermal overload protection 1 49-Thermal overload protection 2 State of external trip function 1 State of external trip function 2 Select settings group Rated Frequency

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 4 of 12

NONEXISTENT NONEXISTENT NONEXISTENT NONEXISTENT NONEXISTENT Line Freq of 60 Hz

The settings above ensure the setting 7821 is set to the correct reference side of the transformer. In the example the overcurrent function is required on the HV side of the transformer.(Comment: ANSI standards recommend a separate overcurrent relay on the HV side for transformer protection. Otherwise, loss of the differential relay results in a loss of main and backup protection for the HV side). There is only one overcurrent element available in the 7UT51 relay, and this element can be used on either winding of the transformer, HV or LV. Set 7816 to the relay reference side 1 if the relay primary winding is connected to the transformer HV winding. Check all wiring against the connection diagrams in the 7UT51 Instruction Manual on Page 186 for the 7UT512 relay, and Page 184 for the 7UT513 relay.

2.2

Insert Transformer Data

The relay uses transformer data to ensure the correct calculation of the differential and restraint quantities. The relay does not require auxiliary transformers to match the secondary currents to the transformer primary currents. These settings are entered into the relay under address block 1100. This address block is found under the Settings tab in DIGSI. Printed settings from DIGSI: 1100 1102 1103 1104 1105 1106 1121 1122 1123 1124 1125 1126

TRANSFORMER DATA Rated voltage of transformer winding 1 Rated apparent power (VA) of winding 1 Rated primary current of winding 1 CT Starpoint formation of winding 1 CT Processing of winding 1 zero sequence current Vector group associated with winding 2 Rated voltage of transformer winding 2 Rated apparent power (VA) of winding 2 Rated primary current of winding 2 CT Starpoint formation of winding 2 CT Processing of winding 2 zero sequence current

13.8 kV 9.4 MVA 600 A Towards transformer Io-elimination 0 *30° 2.4 kV 9.4 MVA 3000 A Towards transformer Io-elimination

The relay uses the settings 1102, 1103, 1104, 1122, 1123 and 1124 to calculate the secondary currents seen by the relay. The relay also needs to calculate the phase angles of the current seen by the relay. This is done using settings 1105, 1125, and 1121. The example in Figure 1 shows that the star point of CT’s are connected such that the star point grounding is facing the transformer. Set 1105 and 1125 to “Towards transformer”. If the transformer star points are grounded 1106 and 1126 must be set to

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 5 of 12

“Io-elimination”. If the starpoint is not grounded 1106 or 1126 can be set to “WITHOUT”. If you are not sure about the grounding condition of a transformer winding set 1106 and 1126 to “Io-elimination”, as this setting works under all circumstances. Figure 1 also shows that the transformer is a delta-delta connected transformer, with no phase shift between the transformer windings. Setting 1121 indicates the connection type of Winding 2, and the phase shift between the reference winding (Winding 1) and Winding 2. Table 4.1 on page 46 of the 7UT51 Instruction Manual lists the settings for a delta connected reference winding. For the example shown in Figure 1, a delta-delta connected transformer with no phase shift, the proper setting is for address 1121 is 0.

2.3

Setting the Differential Function (87)

The relay has a considerable amount of settings for the differential function, found in DIGSI under group address 1600. For most applications, no settings which need to be changed. The default settings are based on long experience with numerical transformer differential relays, and cover nearly every standard application.. However, these settings can be used to alter the relay characteristic curve if necessary. This could be required if a tapchanger has a high regulation range (> +15%, -15%), which is effectively a linear CT-error. Other settings can also be used to set the relay response to inrush current. These setting should remain at default values unless there are information available to justify a setting change. Printed settings from DIGSI: 1600 87-TRANSFORMER DIFF PROTECTION DATA 1601 1603 1604 1606 1607 1608 1610 1611 1612 1613 1614 1615 1616 1617 1618 1625 1626 1627

87-State of differential protection 87-Pick-Up value of diff protection 87HS-Highset Pick-up RMS value of diff prot. 87-Slope 1 of operating characteristic 87-Base point for slope 2 of operating char. 87-Slope 2 of operating characteristic 87-State of 2nd harmonic restraint 87-2nd harm content in the different. current 87-Time for cross-blocking with 2nd harmonic 87-Choice a further (n-th) harmonic restr 87- n-th harmonic content in the diff. current 87-Activ time for cross-blocking w/ n-th harm 87-Limit IDIFFmax of n-th harmonic restraint 87-Max. blocking time at CT saturation 87-Min. restr. current for blocking @CT satur. 87-Trip time delay of diff. current stage 87-Op time of high-set diff. curr stage 87-Reset dly after diff op has been initiated

ON 0.20I/In Trans 7.5 I/In Trans 0.25 2.5 I/In Trans 0.50 ON 15 % 0 *1 Cycle 5th harmonic 80 % 0 *1 Cycle 1.5 I/In Trans 8 *1 Cycle 5.00 I/In Trans 0.00 s 0.00 s 0.10 s

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 6 of 12

Setting 1601 must be set to “ON”. Setting 1603 is set in per unit values and is thus set to 0.20 for a requested setting of 20%. For the HV-side, where the nominal current of the transformer is 393 A, this leads to a sensitivity of 78 A. Calculating the maximum differential current that can be caused by tap changer errors, , can be used to check the setting. The relay is connected to a C200 CT in the example. This CT has a ratio error of not more than 3% between 1 to 20 times of the secondary current if the secondary burden does not exceed 2 ohms. Therefore, the maximum differential current produced by the CT’s if the errors between the LV and HV CT’s are opposing is 3% + 3% = 6% under nominal conditions If the transformer has a tap changer the setting must be increased by 1% for every 1% of tap the changing range. For a setting of 20% the setting must be increased to 30% for a 10% tap change range. So for the example in Figure 1, the required setting of 20% is adequate, because there is no tap changer at the transformer. The setting 1604 is set to a level where a fundamental differential quantity of this magnitude can only be an internal fault. Above this setting the differential relay will issue a trip regardless of the second harmonic setting in 1611. Set this to 7.5 and the relay operates high speed when the fundamental differential current is higher than 7.5. It can be shown, that the fundamental quantity of an inrush is never higher than half of the peak value of the inrush current. Therefore the factory setting covers inrush peak values up to 15 times of nominal current. Inrush peak currents of this magnitude have never been seen in fault records. Setting 1618 is used by the relay to activate the Through Fault Restraint Area. This feature is used to consider the effect of CT saturation on the differential relay. This added security ensures that the relay will not trip under high through fault conditions when CT saturation is more likely to occur. Relays without this feature must increase the second slope (parameter 1608), thereby desensitizing the relay for some fault conditions. The default setting is 7 but we have found that a setting of 5 is more appropriate. The application note Increasing the Security of Low Impedance Differential Protection in Reference [3] describes the relay differential algorithm in greater detail. Settings 1625 and 1626 set the delay times for the 87HS and 87 functions. These settings are normally set to the minimum setting of zero, or no intentional time delay. The following calculations must be done to ensure that the correct CT taps have been used. First calculate the transformer HV primary full load current.

I HV prim =

S 9.4 × 106 = = 393.27 A V × 3 13.8 × 103 × 3

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 7 of 12

Calculate the transformer HV secondary full load current. This is also the relay nominal current referred to the protected object, the transformer.

I HV sec = I HV prim ÷

CT HV prim 600 = 393.27 ÷ = 3.28 A CT HV sec 5

Calculate the transformer LV primary full load current.

I LV prim =

S 9.4 × 106 = = 2261.29 A V × 3 2.4 × 103 × 3

Calculate the transformer LV secondary full load current. This is also the relay nominal current referred to the protected object, the transformer.

I LV sec = I LV prim ÷

CT LV prim 3000 = 2261.29 ÷ = 3.77 A CT LV sec 5

Now calculate the ratio between the rated transformer primary current, and the rated CT primary current, for each transformer winding.

Winding 1 Ratio =

I HV prim 393 = = 0.65 I CT prim 600

Winding 2 Ratio =

I LV prim 2261 = = 0.75 I CT prim 3000

Note: The ratios of the rated primary current to the rated CT primary current must be between 0.25 and 4.00 for each winding. These ratios are always based on the maximum rated power set at addresses 1103 and 1126. This is important, as this effects the accuracy of the differential and restraint calculations.

s 2.4

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 8 of 12

Setting the Overcurrent Protection (50HS and 50/51)

The overcurrent feature of this relay consist of a high set overcurrent function(50HS) and a normal overcurrent function that can be configured to a 50 or a 51 function depending on the selection of setting 2111. These settings are rated to the nominal current of the winding, which is the value of I HV primary calculated previously. Printed settings from DIGSI: 2100 OVERCURRENT PROTECTION ( DTL / IDMTL ) 2101 2103 2104 2111 2112 2113 2114 2115 2116 2118 2121

State of back-up overcurrent protection 50HS-Phase highset (Def. Time) O/C pickup 50HS-Delay time for 50HS ( Def. Time) funct PH O/C time characteristic 50T - Phase (Def. Time) overcurrent pick-up 50T - Delay time for 50T (Def Time) funct 51 - Phase (Inv. Time) overcurrent pick-up 51 - Phase inverse overcurrent time dial Phase current measurement format Reset delay after trip has been initiated Phase overcurrent stage effective :Manual cl

ON 10.16 I/In(_transformer) 0.05 s Very Inverse 2.00 I/In(transformer) 1.40 s 2.03 I/In 1.51 s Without Harmonics 0.10 s Inactive

Calculation of setting 2103. The example requires a pickup value of 4000A primary, which is converted to per unit on the nominal rating of the transformer winding by either of the following methods:

 CT HV prim  600    ÷ I HV sec =  4000 ÷ 50 HS =  I HV prim ÷  ÷ 3.28 = 10.16 CT HV sec  5    OR 4000 4000 50 HS = = = 10.17 I HV prim 393.27 The delay time for 50HS 2104 must be set to 0.05 s as requested. In order to set address 2114 it will be required to convert 800A to a per unit value that corresponds to a multiple of the full load current. We can then use this value to select a curve in address 2111 and time multiplier according the required 10 s delay. Calculate for address 1114.

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 9 of 12

 CT HV prim  600    ÷ I HV sec =  800 ÷ 51 =  I HV prim ÷  ÷ 3.28 = 2.03 CT HV sec  5    OR 800 800 51 = = = 2.03 I HV prim 393.27 For address 2111 select the curve that is suitable for the application so that it coordinates with the downstream protection relays. The curves are found in the 7UT51 Instruction Manual (Reference [3]) on Pages 103 to 105. For the example we selected a very inverse curve. To set the time dial setting 2115 use the curves on Page 104 Figure 8 to select the correct value. The time dial selected is 1.5 for a 10s delay at a current of 2.03 times the full load current or 800 A primary. This setting can also be calculated by using the formula shown on Page 104 for a very inverse curve. Please note that I/Ip is the multiples of the Pickup current and that is the same value that was calculated for address 2114. (51)

TD =

t

 19.138   + 0.48258  2.0  I / Ip − 1  10 TD = = 1.51  19.138  + 0.48258   2.0  2.03 − 1 

The settings for the definite time stage (50T) are not used, as these settings 2112 and 2113 are disabled when a curve is selected under address 2111. These settings are only active when address 2111 is set to definite time. If 2111 is selected to definite time the settings for the 51 function 2114 and 2115 are disabled. Setting 2116 is normally set to “Without Harmonics”, so the relay acts on the fundamental 60Hz current only. If the transformer feeds a rectifier for a steel smelter where harmonics are generated or any other transformer that is likely to see harmonics set this setting to “With Harmonics”.

2.5

Setting Output Contacts and Targets

Relay marshalling sets the functions or events that control all output contacts and target LEDs. The first step before attempting to marshal the required functions to the outputs or inputs is to clear all the default marshalling from the relay. Set all the output contacts,

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 10 of 12

discrete inputs, and LED’s to “No Function Assigned”. After clearing the default configuration, marshal the required functions to the intended relays. The example requires two contacts to be marshalled to trip the HV and LV breakers respectively. Start by marshalling the contact that will be responsible to trip the HV breaker. This contact only opens the HV breaker for trips issued by the 50HS function and the 87 function. DIGSI marshalling example. 6401 Configuration of Trip Relay 1 001 5691 87 -Diff protection: Trip 002 5692 87HS -Diff protection: Trip 003 2441 BU 50HS -Highset O/C time expired 004 0001 No function assigned 005 0001 No function assigned 006 0001 No function assigned 007 0001 No function assigned Marshall the contact that will be responsible to trip the LV breaker. This contact must open the LV breaker for trips issued by the 87, 50HS and 51 functions. DIGSI marshalling example. 6402 Configuration of Trip Relay 2 001 5691 87 -Diff protection: Trip 002 5692 87HS -Diff protection: Trip 003 2442 BU 50/51 -Overcurrent timer expired 004 2441 BU 50HS -Highset O/C time expired 005 0001 No function assigned 006 0001 No function assigned 007 0001 No function assigned The marshalling of the Target LED’s and alarm contacts are performed in a similar manner to meet the end- customers requirements.

3.0

Conclusion

By following this simple example, more complex applications can be implemented on the 7UT51 relays. The implementation of settings on the 7UT51 relays, and all Siemens relays in general, is best performed by creating a relay setting file in the DIGSI software, and using the relay manual for interpretation of settings. The settings can be printed to a text file using

s

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 11 of 12

DIGSI, which can then be inserted into a setting document. The DIGSI file can be given to the customer to load directly to the relay. Although the 7UT51 relay provides the customer with numerous settings, only a few settings must be calculated and changed from the default settings for almost all application requirements. The default settings of the relay can protect all type of threephase and single-phase transformers. Normally only setting the transformer and CT data is required. The differential settings remain unchanged, except to switch ON the 87 function.

s 4.0

TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00

Page 12 of 12

References

[1] 7UT51 V3 Protective Relay Instruction Manual, Siemens Power Transmission & Distribution, Inc., Raleigh, NC; 1999 [2] 7UT51 V3 Transformer Differential Relay Acceptance Testing, Commissioning and Maintenance Manual, Siemens Power Transmission & Distribution, Inc., Raleigh, NC; 1999 [3] Increasing the Security of Low Impedance Differential Protection, Siemens Power Transmission & Distribution, Inc., Raleigh, NC; 2000

Siemens Power Transmission & Distribution Inc. Distribution Automation Division P.O. Box 29503 ! Raleigh, NC 27626-0503 Tel: (800) 347-6659 ! Fax: (919) 365-2552 ! [email protected]