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2016 International Conference on Condition Monitoring and Diagnosis - Xi'an - China

Feasibility analysis of impedance monitoring method for Turn-to-turn Insulation Fault of Dry-type Air-core Reactor Hong L1U,Yonghong WANG,Ziwei G AO,Xuecheng ZHU Harbin University of Science and Technology,Heilongjiang Electric Power Research Institute Harbin 150080,150030 Heilongjiang Province, China Email:[email protected] [email protected] Abstract-Dry-type Air-core Reactor consists of multi-layer

ection and unbalanced three-phase protection method,the turn­

coils and Multi-strand windings.The change of impedance value

to-turn fault of dry-type air-core reactor cannot be detected in

caused by turn-to-turn insulation fault of dry-type air-core rea­

time.!n general,turn-to-turn insulation fault cannot be found

ctor is so little that the over current protection and Three-phase

until the reactor appears smoke,even fire burning,and the

imbalance protection can't act timely.In order to monitor turn­

turn-to-turn insulation fault develops into phase-to-phase short

to-turn insulation fault of reactor , a new monitoring method ba­

circuit or phase-to-ground short circuit.Therefore, it is necess­

sed on impedance variation is proposed in this paper. Takes

ary to carry out research on the dry-type air-core reactor

reactor BKK-20,OOO/63 for an example to study the relation

protection.

between the variation of impedance value and the turn-to-turn

At present,the technology of oil-immersed type reactor

insulation fault position of dry-type air-core reactor. The result

protection is relatively mature ,and commonly used method is

shows that the change of equivalent reactance value caused by

through comparing the zero sequence compensation voltage of

turn-to-turn insulation fault is little,while the change of equi­

end with the zero sequence voltage of head-end of the reactor

valent resistance value is large. The closer the axial fault to both

to detect turn-to-turn fault, which is not applicable for dry­ type air-core reactor[2-31.Some scholars put forward a protec­

ends is, the larger the variation is. Along with the radial fault location, variation of outer is larger than inner's. Method based

tion method,which is based on variation of voltage ratio ,for

on the variation of resistance to monitor the turn-to-turn insul-

the turn-to-turn fault of dry-type series reactor. The ratio of

ation fault of dry-type air-core reactor is feasible. Besides,the rel­

the voltage on the capacitor and reactor is a constant value

ative monitoring method based on loss or tangent of dielectric

under normal circumstances,which will change when there is a short circuit fault on the reactor[4-51. It is not applicable for

loss angle is reasonable.

dry-type air-core reactor either.There is no mature protection

Keywords: Dry-type air-core reactor; Turn-to-turn insulation;

methods and techniques for the dry-type air-core reactor at

Monitoring; Impedance variation

present. 1.

INTRODUCTION This paper analyzes the variation of electrical parametes

Dry-typr air-core reactor has advantages of simple stru­

of dry-type air-core reactor,when reactor turn-to-turn insulat­

cture,light weight,convenient maintenance,etc,Which is used

ion fault happens,and discusses the monitoring method of turn

to balance the reactive power and improve the voltage quality in the electrical power system[11.However,the fault incidence

-to-turn fault of dry-type air-core reactor based on it. II.

rate of dry-type air-core reactor is higher than the transformer and other equipments' under the same voltage grade. A large

(1) Equivalent circuit

amount of data analysis indicates that the main eason of

Actually, multi-layer reactor turn-to-turn insulation fault

dry-type air-core reactor fault is turn-to-turn insulation fault.

circuit that occurs in the early stage is strand-to-strand insu­

Currently, due to the low sensitivity of overcurrent prot-

978-1-5090-3396-6/16/$3\.00 ©2016 IEEE

CALCULALATION METHOD

lation fault. Under the condition of power-frequency , dry-

152

type air-core reactor is combination of multi-parallel branches,

p(2nRini + hi)

each branch has a DC resistance, self inductance and mutual

n

inductance. A reactor is provided with n layers, and each layer is provided with m strand coils. When a short circuit occurs in the i-th layer of the strand coils, the coil can be divided into 2

eter of aluminum wire, h;is the height of layer coil.

it of tum-to-tum insulation fault reactor,which consists of n-J branch based on layer coil and I branch based on strand coi­

(3) Voltage equations

I,as shown in figureI-I.R; and L; respectively represent bra­

When the reactor is applied to the voltage U , and each

nch resistance and self inductance, mutual inductance exists between each branch.As shown in Figure1-1.

i,

R,

R�

(;

L,

r

i

. R,,

U,

L2

L,

RQ

t

io

i.

O J Ro [ R

LB •

R" LA

[;,

r' "

J

LiS

(3)

Wherep is the resistivity of aluminum wire, d)s the diam

short circuit units and the remaining unit.The equivalent circu­

i,

( ; )2

branch current is Ii ,the voltage matrix equation of equivalent

in-1

i,

R"j

R;IJ

circuit under normal condition can be obtained by the formula(4) RI + jeoLI jeoMIl .. , jeoMl,; .. , jeoM21. R2 + jeoL2 .. , jeoM2; .. ,

L,

L",

jeoMI,. jeoM2;

i, i2

U

jeoM;2 .. , jeoM",J .. , R" + jeoL" j"

U

U

ii4 jeoM;J

Fig.l-l The equivalent circuit of dry-type air-core reactor

(4)

When the strand-to-strand fault occurred between coils,

(2) Parameter calculation method

the fault coils are divided into five parts, the circuit equations

Neumann formula can be used to calculate mutual

as follows:

inductance between each coil.

. . . . jOJMn.JI +"'+(�I + jOJLn)Jn +... + jOJMn.in =U1 .

.

.

.

jOJMi2il +"'+(�2 + jOJLi2)Ii2 +... + jOJMi2.in =U2 (1) Where,

Z, ,

HI 2

H2 2

=----

+S

,

Z

4

H

1

= __

2

H

.

+_2 +S

Ii!

2

.

Ii

Coil self-inductance can be calculated by the formula(2). L

=

2Jlon2R2 [F(R,R,H)-F(R,R,O)]

. + =

Ii3

=

.

Iii

.

Ii2

. +

. +

Ii2

Ii4

.

+

(5)

Ii5

(4) Calculation ofImpedance

(2)

Tolal Current of reactor can be calculated by sum of each

Where, Rj and R2 are the two radius of coils,HjandH2are

layer current.

the heights of coils,njandn2are the numbers of tums.xjandx2are the distances from two coil turns to the center of the coil,1l ois

(6)

vacuum magnetic permeabilitY,and S is the distance between two coils center.

Total impedance can be calculated by the formula(7).

The coil conductor resistance depends on the size of the conductor geometry size,which can be obtained by the formu­ la(3). 153

when strand-to-strand short circuit occurs at the end is larger

U Z=----;-= R+ jX I ·

than on other heights of reactor. All statistical results shows (7)

that the variation of the layer coil current is in the range of

Equivalent resistance and equivalent reactance are given

-4.63%�3.61%, and variation of layer coil current is larger than the total current .Take the 41-th layer coil as an example,

by formula(8)

layer coil current variation of a short circuit occurred on

R = ReCZ)

different heights of the reactor is shown in Figure 2-2 .

X = ImCZ)

(8)

The current and the equivalent impedance can be calcul­ ated by Matlab software. III.

THE RESULAT OF CALCULATION

(1) Reactor impedance check

This paper takes a BKK-20000/63 reactor as an example

Sequence of Laycr coils

to calculate,which is composed of 11 packages, 49 layers of coils, and each layer of coil is made up of 2 strands of wires in

Fig. 2-2The relative variation of layer coil current

parallel. Factory provides a detailed structural parameters about the reactor.

With a strand coil as a unit, the variation of short circuit

According to the formula (4), the impedance value of the

strand coils current as shown in figure2-3. Strand coils current

faultless reactor is 67.9483. Factory-fresh reactor impedance

changes significantly, and two groups of them are in pairs for

is 68.1196, and the calculated value error is 0.25%.

that short circuit circles formed in the side of coils. The biggest changes in the amount can up to 10424.

(2) Result of current calculation

12(){){)

Take l-st, ll-th, 21-th, 31-th, 41-th, 49-th layer coils

---'-i l-coil

(from the inside to the outside)of reactor for short circuit

_i2_coil """-i3-coil

analysis.When the reactor is applied the rated voltage,and

_i4_coil

short circuit respectively occurs at the coil 0 (end), 1/8, 1/4, 3/8 and 1/2 at the height (Center)of reactor, the total coil current variation as shown in figure 2-1. When short circuit occurs at the end of the coil, the change of the total current is the largest, with the short

0.00

position of the short circuit moving to the center, the change

0.13

Positon of short ci rcuit 0.25

0.38

0.50

Fig.2-3 The relative variation of strand current

of value decreases rapidly. Besides,the total current variation (3) Impedance calculation

of outer layer is larger than the inner layer's. However, the

According to formula (8), The equivalent resistance and

change of total current value of reactor is very little, the

reactance variation of reactor when strand-to-strand short

maximum value is