THE PRINCIPLES OF RELAY PROTECTION IN PROTECTIVE METHOD

Select protection for transformers B1, B2 and line L 1 Tra bảng Sổ tay tra cứu các thiết bị điện từ 0,4-500kV, Ngô Hồng Quang 3TIEU LUAN MOI download : skknchat123@gmail.com... CHAPTER 3

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CHAPTER 1 : SELECT THE CURRENT TRANSFORMER 5

1.1 SELECT BI FOR LINE PROTECTION (BI7) 5

1.2 SELECT BI FOR TRANSFORMER PROTECTION 6

1.2.1 Select BI1 (BI4) 6

1.2.2 Select BI2 (BI5) 6

1.2.3 Select BI3, BI6 6

CHAPTER 2: METHOD OF PROTECTION 7 2.1 METHOD OF PROTECTION FOR TRANSFORMER 7

2.1.1 The type of faults and abnormal working mode 7

2.1.2 Method of protection 7

2.2 METHOD PROTECTION FOR LINE 8

CHAPTER 3: THE PRINCIPLES OF RELAY PROTECTION IN PROTECTIVE METHOD9 3.1 RESTRAINT-DIFFERENT RELAY PROTECTION 9

3.1.1 The principle of restraint-different relay protection 9

3.1.2 Restraint differential relay protection 10

3.2 BUCHHOLZ RELAY PROTECTION 12

3.3 TIME OVERCURRENT RELAY 13

3.4 OVERCURRENT ZERO SEQUENCE PROTECTION 14

3.5 OVERLOAD TRANSFORMER PROTECTION 14

CHAPTER 4: CALCULATION OF SHORT CIRCUIT 16 4.1 CALCULATION OF REACTANCE VALUE 16

4.1.1 Calculation of reactance value of element in maximum power system mode 16

4.1.2 Calculate the resistances in the minimum system capacity mode 17

4.2 CACULATE SHORT-CIRCUIT CURRENT 18

4.2.1 Calculate short-circuit current in maximum system power mode 18

4.2.2 Calculate short-circuit current in minimum system power mode 24

CHAPTER 6: CALCULATE PROTECTION FOR LINE 27 6.1 SHORT-CIRCUIT CURRENT IN SOME CASES ON LINE L 27

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6.1.1 Instantaneous overcurrent relay protection 27

6.2 MAXIMUM OVERCURRENT RELAY 29

6.2.1 Maximum power system mode 29

6.2.2 Minimum power system mode 30

6.3 CALCULATE ZERO PROTECTION (TTK) 30

CHAPTER 7: CHECK THE WORK OF PROTECTION FOR THE SUBJECTS 32

7.1 CHECK THE WORK OF THE TRANSFORMER PROTECTION 32

7.1.1 Check the work of the transformer protections compare offset current with braking 32 7.1.2 Check the work of over fast cutting current 34

7.1.3 Zero sequence in earth fault ( TTK) 34

7.2 CHECK THE WORK OF THE PROTECTIONS IN THE LINE 35

7.2.1 The instantaneous overcurrent 35

7.2.2 Maximum current protection 35

7.2.3 Zero sequence in earth fault (TTK) 35

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RELAY PROTECTION PROJECT Code: 43554B

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III Performance requirements

1 Select BI for protection

2 Select protection for transformers B1, B2 and line L

1

Tra bảng Sổ tay tra cứu các thiết bị điện từ 0,4-500kV, Ngô Hồng Quang

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3 The principles of relays protection

earth fault protection for transformers

not set for line L

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CHAPTER 1 : SELECT THE CURRENT TRANSFORMER

Conditions to select BI:

The rated voltage:

With:

manufacturer

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1.1 Select BI for line protection (BI7)

The maximum current working through the line L :

5

1.2 Select BI for transformer protection

1.2.1 Select BI1 (BI4)

maximum current flows through BI1 :

5

300

5 1.2.2 Select BI2 (BI5)

Considering the overload condition of the MBA, the maximun current flows

through BI1 is:

IBI1max=kqt x

S dmB 1

= 1,4

40

√3 U Hdm √3 22

Select BI has the rated primary current 1500 A and the rated second current 5A,

5

1.2.3 Select BI3, BI6

5

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CHAPTER 2: METHOD OF PROTECTION 2.1 Method of protection for transformer

2.1.1 The type of faults and abnormal working mode

Fault types can be divided into two groups: internal faults and external faults:

- Short-circuit winding fault

- Touch ground (short circuit) and short circuit

ground - Breakdown of voltage divider

- Oil tankers (oil leak)

2.1.2 Method of protection

Function : main protection for transformers

- Protection area: against all types of faults inside the transformer

Multi-phases inside transformer

overcurrent protection

- Function :

+ Remove short-circuit faults occuring inside and outside transformer - Protection area :inside in transformers and a part outside

- Note :

protections

orientation at the connection to the source having smaller impact time

one end of the transformer, near the source (because if one coil is overloaded then

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the remaining coil of the transformer is overloaded too) If there is a transformer with multiple windings, each side must have one set

overload fault

- Protection area :

Figure 2.1 Diagram of protection mode for

transformers 2.2 Method protection for line

Line L is a medium voltage line, so we need to put protection against short circuits,touching on the line We use time overcurrent relay (50) as the main protection(Inverses-Time Overcurrent), instantaneous overcurrent relay (51) as redundancy

To detect and prevent ground faults on line L, use zero overcurrent relay (50N,51N)

Figure 2.2 Diagram of protection mode for line

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CHAPTER 3: THE PRINCIPLES OF RELAY PROTECTION IN

PROTECTIVE METHOD 3.1 Restraint-different relay protection

3.1.1 The principle of restraint-different relay protection

element

given value (threshold current):

The protective zone of the differential protection is limited by the position of thetwo current transformers at the begin and the end of the protected element, fromwhich the current signal is received for comparison

Figure 3.1.1 Differential relayprotection

In theory =0 However, reality may be different 0 by the effect of unbalancedcurrents by some of the following reasons:

or short circuit outside has large value in the short time

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The threshold current is defined as follows:

: the largest external short circuit

3.1.2 Restraint differential relay protection

Restraint differential relay protection is differential relay has been added restraint element to increase the sensitivity and reliability of the protection

(With conventional dimension from the busbar to the line)

Figure 3.1.2 Restraint differential relay protectionThreshold current of restraint differential relay has changes when the current in

branch of the protection circuit The comparator part of the relay compares the

absolute value of the two currents

current, the relay does not work

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Figure 3.1.3 Deviation angle between IT1 và IT2 because error of BI

Figure 3.1.4 The impact area of differential protection + Characteristic segment (a):

The low threshold current difference indicates the low current value of the deviationprotection (due to the effect of an unbalanced current in normal operation mode) Ifthe line (a) is too high it will reduce the sensitivity, the low (a) line will cause thewrong effect

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Characteristic for high value deviation.

When the current deviates from this value, the protection will act regardless of the restraint current

is usually set at a level when the short circuit at the transformer output and fault

3.2 Buchholz relay protection

and the level of oil drop is too much

of the MBA The two-level relay consists of two glass-bulb metal buoys with a mercurycontact or magnetic contact In normal working mode in full oil tank, floating buoys in oil,relay contacts are in open state

Figure 3.2 Buchholz relay

generated, which will accumulate in the lid of the Buchholz relay When the amount of gasaccumulated is large enough, it will sink the float and close the contact, the relay sends alevel 1 warning

gas generated is very large, forming a stream, passing through the relays to the expansiontank At that time, the bottom float is submerged, the bottom is closed

Contact under the impact when the incident is severe It is arranged to cut the transformer

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- Protection has two levels: light - signaling and heavy - cutting.

the regulator load box, when there is a problem in this set, the oil is heated, will move into astream, causing the relay to move, cut transformers

3.3 Time overcurrent relay

protection device increases beyond the thresold value Time overcurrent relays ensureselectivity by selecting the working time according to the principle of each

level, protection closer the relay is to the source, the greater the impact time

Principle :

I ≥ Ikd

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Figure 3.3 Time overcurrent protectionThresold current for protection:

through the protection element:

with:

digital relays

- Ilvmax : maximum working current of line

Thresold current of secondary side:

with

Impact time :

Coordinate with neighborhood protections on the principle of step-by-step ladder

3.4 Overcurrent Zero sequence protection

I0 >

Figure 3.4 Overcurrent Zero sequence protection

of action is also the effect when the zero sequence current does not exceed the thresoldvalue :

I0 ≥ Ikd

at the neutral of the transformer

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3.5 Overload transformer protection

- Overloading increases the temperature of the transformer, if the high and term overload, the transformer is overheated, the life of the transformerdeteriorates rapidly In order to protect against overloads of power transformersyour baby can use conventional overcurrent protection Overcurrent protectionuses current relay with the function of protecting the overload signal oftransformer

overload This type of protection reflects the temperature rise at different test points in thetransformer and depending on the temperature increase range, there are many differentlevels of action: warning, starting with increased cooling levels (air or oil), reducetransformer load If the impact levels are not effective and the transformer temperature stillexceeds the permitted limit and the specified time is extended, the transformer will be cutoff the system

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CHAPTER 4: CALCULATION OF SHORT CIRCUIT

4.1 Calculation of reactance value

Basic voltage equal to average voltage at voltage level:

4.1.1 Calculation of reactance value of element in maximum power system mode

Subtation has two parallel transformers:

- Positive sequence schema:

- Negative sequence schema:

The same positive sequence schema but don’t have E:

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- Zero sequence schema:

X 10 = 1,15 X 11 = 1,15.0,011 = 0,012

X 20 = X 21 = 0,072

X 30 = 2,8.X 31 = 2,8.0,039= 0,109

4.1.2 Calculate the resistances in the minimum system capacity

mode Power of system: S HT = 1700 MVA

Transformer station operates with 1 transformer

- Diagram of positive:

S cb

- Negative sequence schema:

The same positive sequence schema but don’t have E:

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- Zero sequence schema:

X’ 10 = 1,15 X’ 11 = 1,15.0,015 =

X’ 30 = 2,8X’ 31 = 2,8.0,039= 0,109

4.2 Caculate short-circuit current

The all short circuit point:

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4.2.1 Calculate short-circuit current in maximum system power mode

Short-circuit types to consider:

N (1,1)- Double phase short circuit with ground connection

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Short circuit current at N 2 , N 2 ’

The total resistance positive, negative, zero when the short circuit at the point N2:

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Short circuit current at N 3

The total resistance positive, negative, zero when the short circuit at the point N3

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At point N4, N5, N6 Similar calculation we have:

Table of short circuit of max mode with 2 transformer working in parallel

b) 1 transformer works independently Short cirtcuit current at N1, N1’

The same in 2 transformer mode works in parallel

Short cirtcuit current at N 2 , N2’

The total resistance positive, negative, zero when the short circuit at the point N2 :

XN22 = XN21 = 0,083

- Short cirtcuit N (3)

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Similar calculate, we have:

Table of short circuit of max mode with 1 transformer working

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I0 (1) 88,23 12,00 10,11 8,73 7,69 6,86

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INa1 (1,1) 59,88 8,02 6,98 6,2 5,58 5,08

4.2.2 Calculate short-circuit current in minimum system power mode

The type of short circuit:

N (1,1)- Double phase short circuit with ground connection

The total resistance positive, negative, zero when the short circuit at the point N1

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Table of short circuit of min mode with 2 transformer working in parallel

The same in 2 transformer mode works in parallel

Short cirtcuit current at N 2 , N2’

The total resistance positive, negative, zero when the short circuit at the point N2 :

X’N22 = X’N21 = 0,087X’N20 = X’10 + X '21 = 0,017 + 0,072 = 0,089

- Short circuit N (2)

X ' N 2Δ =X ' N 22Σ =0,087

Short circuit current at N2:

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Table of short circuit of min mode with 1 transformer working

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IN (1) 63,83 11,41 9,69 8,42 7,44 6,67

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I0 (1) 63,83 11,41 9,69 8,42 7,44 6,67

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CHAPTER 6: CALCULATE PROTECTION FOR LINE

6.1 Short-circuit current in some cases on line L

The resistance of transformer when two transformers work in parallel in half when a

transformer works independently Therefore, the largest short-circuit current on

the line when a short circuit occurs will be the max system power mode and two

transformers work in parallel The smallest short-circuit current on the line when a

short-circuit occurs on the line will be the min system power mode and 1

transformer works independently

Table 6.1 Short-circuit currents in max system power mode, 2 transformers:

We calculte instantaneous overcurrent relay, maximum overcurrent relay, zero

overcurrent relay prrotection for line L

6.1.1 Instantaneous overcurrent relay protection

with: kat – safety factor, kat = 1,2

I Nngmax – The maximum external circuit current is the largest circuit current that is usually equal to the short-circuit current value of the bar on the end ofline

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short The external short-circuit current of line L:

= 1,2 9,01 =10,81

Protect area of instantaneous overcurrent relay

30 25 20

15 Max shortcircuit current

Min shortcircuit current Threshold current 10

- The largest protection area: (Lmax)

Trong đó:

The largest protection area:

29

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1 0,072 2

= [ 10,81−(0,011+ 2 )]. 25.0,15423 = 6,25(km)

6,25 100%= 89,29%

7

=> Protect for 89,29% of line

6.2 Maximum overcurrent relay

6.2.1 Maximum power system mode

The threshold current :

with: kat –Safety factor, kat = 1,2

kmm – Open factor, kmm = 2

kv - Return coefficient selected for digital relay: kv = 0,95

Ilvmax- The largest working current, Ictlvmax = 238,57 A

Convert maximum working current to relative unit system:

with : TMS: constant time set of relay (s)

30

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- Short circuit point N6: IN6 max = 9,01

Similar calculations for short circuits on the line we have

Table 6.3 Impact time of the max system

6.2.2 Minimum power system mode

Table 6.4 Impact time of the min system

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CHARACTERISTICS OF THE TIME OF OVERCURRENT PROTECTION

t max mode t min mode 003

000

6.3Calculate zero protection (TTK)

-Threshold current of protection

The working time of overcurrent protection does not have time to select according

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