CN106786384A

CN106786384A - Generator transformer formula L-R type neutral earthing devices

Info

Publication number: CN106786384A
Application number: CN201510821390.3A
Authority: CN
Inventors: 姚建平
Original assignee: HARBIN YAYUAN ELECTRIC CO Ltd
Current assignee: HARBIN YAYUAN ELECTRIC CO Ltd
Priority date: 2015-11-24
Filing date: 2015-11-24
Publication date: 2017-05-31

Abstract

Generator transformer formula L-R type neutral earthing devices are applied to large and medium-sized synchronous generator neutral ground protection.With China's power system development; single-machine capacity is improved constantly; capacitance current constantly increases; be limited in earth-fault current in allowed band, it is necessary to take a kind of rational earthing mode by most of unit earth-fault currents permissible value more than 15A; when there is singlephase earth fault in generator; the protection to generator stator core is realized, and then prevents stator winding insulation to be destroyed, it is to avoid cause alternate or turn-to-turn to be short-circuited.

Description

Generator transformer formula L-R type neutral earthing devices

Technical field：The present apparatus is applied to large and medium-sized synchronous generator neutral ground protection.When generator occurs singlephase earth fault, the protection to generator unit stator winding overvoltage and iron core is realized, and then prevent stator winding insulation to be destroyed, it is to avoid cause alternate or turn-to-turn to be short-circuited.

Background technology：As China's power system development, single-machine capacity are improved constantly, electric capacity constantly increases, and capacitance current also increases therewith, indivedual unit earth-fault current I_fMore than 50A, greatly threat is brought to generator stator core.The requirement more and more higher to large and medium-sized synchronous generator grounding protection device of neutral point is caused, neutral ground fault current and stator winding overvoltage are limited within the specific limits when just necessarily requiring generator singlephase earth fault.For reasonable, the correct selection of this neutral grounding mode becomes more important.Common practice in industry is that generator neutral point is grounded through grounding through arc or through Circuit Fault on Secondary Transformer connecting resistance mode.Grounding through arc mode can reduce earth-fault current, but significantly have the disadvantage that fault detect is difficult and parallel resonance easily occurs.It is grounded through Circuit Fault on Secondary Transformer connecting resistance mode, when can limit generator singlephase earth fault, perfects the instantaneous overvoltage of phase no more than 2.6 times, for protecting of stator provides power supply, it is easy to detect.According to《Power engineering electrical design handbook electrical primary》The purpose " the purpose is to add appropriate resistance in capacitor loop; to limit during generator singlephase earth fault; perfect the instantaneous overvoltage of phase no more than 2.6 times of specified phase voltages, and limitation earth-fault current as far as possible is no more than 10~15A " of P265 pages of installing grounding transformer and resistance.When Circuit Fault on Secondary Transformer connecting resistance earthing mode is used, when earth-fault current is excessive, stator core damage is easily caused, it is impossible to which be limited in earth-fault current within 15A by satisfaction, such as takes no action to, very risky.Based on the deficiency of both the above earthing mode, my company have developed a kind of generator transformer formula L-R type neutral earthing devices.

The content of the invention：The purpose of the present apparatus is to provide a kind of generator transformer formula L-R type neutral earthing devices.

Generator transformer formula L-R type neutral earthing devices complete units include：The parts such as cabinet, high voltage isolator K, grounding transformer T, grounding resistor R, ground inductor L, low-pressure side overvoltage protection HY, Current Transmit 1 and Current Transmit 2.

Design principle：Present apparatus design principle changes traditional neutral point the design of grounding thought.It is combined by grounding through arc and through Circuit Fault on Secondary Transformer connecting resistance earthing mode, i.e., grounded transformer grounding, Circuit Fault on Secondary Transformer connecting resistance shunt inductance, using inductive current I_LNThe too high capacitance current I of compensation_C, through the capacitance current I after inductance compensation_C-I_LNAs reactive current, the watt current I produced with earth resistance_RN, collectively constitute generator earth-fault current I_f：

I_LN-- it is folded to the inductive current of transformer primary side；

I_RN-- it is folded to the resistor current of transformer primary side.

According to DL/T 5090-1999《Hydraulic power plant's overvoltage protection and Insulation Coordination designing technique directive/guide》In " 4.5 high resistance " related content, generator neutral point access resistance value size, will influence generator neutral point temporary overvoltage value.It is 1.5 times of rated voltages by the pressure voltage of operating unit, then perfects phase temporary overvoltage no more than 2.6 times of phase voltages.To meet requirements above, then resistor current is not less than capacitance current during generator single-phase earthing.

According to《Large-scale electromechanical relay protection theoretical foundation》P226 pages, " singlephase earth fault watt current will be equal with capacitance current, and general capacitance current is no more than 10A so that singlephase earth fault total current is less thanMeet the requirement no more than 15A ".

The design requirement is through the capacitance current I after inductance compensation_C-I_LNLess than 10A, the electric current I that earth resistance passes through_RNValue with through the capacitance current I after inductance compensation_C-I_LNIt is equal, you can by earth-fault current I_fIt is limited within 15A.Retain two kinds of advantages of earthing mode simultaneously, solve the problems, such as that grounding through arc mode is also easy to produce resonance and detection difficult, also solve the earth-fault current problems of too that simple resistance grounded brings.By inductor design in Circuit Fault on Secondary Transformer, the rated voltage of inductance is reduced, reduce the cost of inductance, reduce the volume of inductance.Generator transformer formula L-R types neutral earthing devices major loop electrical schematic diagram is as shown in figure 1, generator transformer formula L-R type neutral earthing devices appearance schematic diagrams are as shown in Figure 2.

The advantage and feature of the present apparatus：

(1) generator neutral point earth-fault current is limited within 15A；

(2) avoid earth-fault current it is big to a certain extent when earth point electric arc be unable to automatic distinguishing；

(3) protection generator unit stator winding and iron core are not damaged by；

(4) simple grounding through arc mode is avoided to produce parallel resonance；

(5) allow generator band single-phase earth fault current to run a period of time (being usually no more than 2h), improve system reliability, be that failture evacuation gains time；

(6) phase overvoltage will be perfected and is limited in less than 2.6 times；

(7) for protecting of stator provides power supply, it is easy to detect；

(8) high voltage isolator division state possess on the spot, teletransmission warning function；

(9) debug simple, easy to maintenance, safe and reliable.

Brief description of the drawings

Fig. 1 is the major loop electrical schematic diagram of the present apparatus.

Fig. 2 is the appearance schematic diagram of the present apparatus.

Wherein " 1 " is device label；" 2 " are cabinet；" 3 " are indicator lamp；" 4 " are indicator lamp nameplate；" 5 " are observation window；" 6 " are disconnecting switch handle；" 7 " are Warning board；" 8 " are device nameplate.

Specific embodiment

The total direct-to-ground capacitance of generator neutral point：

C=3 (C_of+C_t) (1-1)

C_of-- the single-phase direct-to-ground capacitance of generator unit stator winding (μ F)

C_t-- in addition to generator, other equipment (main transformer, GCB, enclosed busbar, unit transformer etc.) single-phase direct-to-ground capacitance (μ F) does not provide C as user in generator loop_tWhen, (0.15~0.5) C can be chosen according to design experiences value_of(this data need to be examined through user).

The total capacitive earth current of generator

U_N-- generator line voltage (V)

According to《Large-scale electromechanical relay protection theoretical foundation》P226 pages, " singlephase earth fault watt current will be equal with capacitance current, and general capacitance current is no more than 10A so that singlephase earth fault total current is less than 2 × 10A of √, meets the requirement no more than 15A ".Determine that generator neutral point earth-fault current amplitude is required less than the present apparatus is met by 15A^。Now with selectionAs a example by, introduce the choosing method of each component.According toThen resistor current is equal with the capacitance current after compensation again, i.e. I_C-I_LN=I_RN=10A.Thus I can also be calculated_LN=I_C-10A。

Transformer primary side voltage U₁It is chosen for generator line voltage U_N, secondary side voltage U₂It is typically chosen in 220V or is required to choose according to user.Understand transformer voltage ratio N=U_N/U₂。

The selection of earth resistance：

According to I_RN=10A, can calculate earth resistance rated current I_R=NI_RN.Then earth resistance resistance：

The selection of grounding transformer：

Transformer primary side load current value：

Transformer rated capacity is calculated：

S_TN=U_NI_1N (1-5)

Grounding transformer is advisable with choosing epoxy cast dry single-phase transformer.It is determined that during the capacity of final selection, can be by the time of ground protection action tripping operation, using the capability of overload of transformer.Capability of overload can be by IEEE Std C62.92.2^TM- 1989 (R2005) choose：

Overload time	Capacity overload multiple
		10s	10.5
60s	4.7
		10min	2.6
30min	1.9
		2h	1.4

The selection of grounded inductor：

According to I_LN=I_C- 10A, can calculate grounded inductor rated current I_L=NI_LN.Grounded inductor value：

Examined by user after the other specification of capital equipment and the parameter of other equipment can be chosen by user's requirement, or we chooses.

Claims

1. generator neutral point is combined through grounding through arc mode and grounded transformer secondary connecting resistance earthing mode, generator neutral point is through connecing Ground transformer grounding, grounding transformer secondary side connecting resistance, on a resistor shunt inductance.Using inductive current I_LN(it is folded to transformer primary side Current value) compensate too high capacitance current I_C, through the capacitance current I after inductance compensation_C-I_LNIt is active with what earth resistance was produced as reactive current Electric current I_RN(being folded to transformer primary side current value), collectively constitutes generator earth-fault currentAnd by earth-fault current I_fIt is limited within 15A.