CN104348178A - Realization method for reducing HVDC outage caused by AC system secondary harmonic wave - Google Patents

Abstract

Provided is a realization method for reducing HVDC outage caused by AC system secondary harmonic wave. The method comprises the steps that positive sequence and negative sequence characteristics are detected at an AC side; and conventional 100Hz protection is modified, the optimized 100Hz and the additionally arranged 150Hz protection is isolated, and influence of AC side secondary negative sequence harmonic wave on a DC side can be precisely processed by the two types of protection. Outage probability is reduced via adjustment of action current and an action time setting value, and a load can be transferred to the other pole via outage of one pole firstly even the action needs to be off. The lower limit of the action setting value is confirmed according to continuing and interruption of DC current through detection, and harmonic wave endurance capacity of electrical equipment of a converter station is considered in confirmation of an upper limit setting value; original 50Hz protection is also correspondingly adjusted so that the protection actions inside and outside the area can be better distinguished, and influence of AC side secondary positive sequence harmonic wave can be more precisely coped. Outage influence on the HVDC caused by AC system secondary harmonic wave can be reduced so that the number of times of outage is obviously reduced and outage loss is reduced.

Description

A kind of implementation method reducing AC system second harmonic and cause HVDC to stop transport

Technical field

The present invention relates to a kind of method reducing AC system second harmonic and cause HVDC to stop transport, belong to the optimization of protection system.

Background technology

After high-power transformer maintenance, air-drop is closed a floodgate and is charged, and produces very large magnetizing inrush current, can produce very large harmonic wave, mainly secondary Negative sequence harmonic in net side.For the weak AC system in NORTHWEST CHINA area; too strong electrical network is not had to support; easy generation second harmonic transmission is amplified; and Northwest Grid is connected to DC engineering more; second harmonic is delivered to direct current system easily via converter valve; as shown in Figure 1, the triple-frequency harmonics of direct current system is increased suddenly, cause protection act to be forced to one pole or bi-pole protection block.

In order to protect direct current system to affect from low-order harmonic, the mainly 100Hz protection of current direct current system, mainly as AC system, the backup protection of direct current system during single-phase or phase-to phase fault, avoids occurring between interconnected network that continuous power vibrates.100Hz protects the harmonic current sampling bandwidth of original design to be 80Hz ~ 200Hz, includes 2 times and 3 subharmonic, protection act when harmonic current is larger.This protection range is comparatively large, and accuracy is poor, often causes unnecessary action.

In addition, when there is secondary positive sequence voltage in converter valve pulse-losing and AC system, all can produce the first harmonic electric current of 50Hz in DC side, occur 50Hz power oscillation.The object that customary DC engineering 50Hz protects is the backup protection of losing pulse as converter valve, is called in district and protects.When 2 subharmonic positive sequence voltage appears in AC system, there is 50Hz power oscillation in direct current, and 50Hz protection also can action, is called outside district and protects.Protect object to be between interconnected network, occur that continuous power vibrates outside district, power network safety operation in harm Tibetan, ensure that direct current equipment of itself is not endangered simultaneously.

For the light current net being similar to NORTHWEST CHINA electrical network, local power grid is more weak, and is connected to high voltage direct current transmission project simultaneously.Be easy to because the impact of AC system second harmonic causes locking to stop transport.Therefore necessary invent a kind of can accurately process each harmonic impact protection system, ensure power grid operation.

Summary of the invention

The object of this invention is to provide a kind of implementation method avoiding AC system second harmonic to cause HVDC to stop transport.The method better can process the HVDC stoppage in transit problem because AC system second harmonic causes, to direct current system once, secondary, triple-frequency harmonics detect accurately and process.

Technical scheme of the present invention comprises the steps:

(1) detection bandwidth that the 100Hz of HVDC DC side protects is adjusted to 80Hz ~ 120Hz from 80Hz ~ 200Hz.As shown in Figure 2.

(2) original 100Hz protective current setting value is constant, and after time setting value considers direct current one pole fault, another pole power turns generation success; effectively can reduce bipolar probability of simultaneously stopping transport; therefore the two poles of the earth protection should adopt different trip time, i.e. an extremely first action, another extremely rear action.Advise that a pole trip time is 3 seconds, another pole trip time is 6s.

(3) arrange separately 150Hz protection, Harmonic currents detection Bandwidth adjustment is 130Hz ~ 170Hz, as shown in Figure 3.

(4) as newly-installed protection; if detect that AC second harmonic is negative phase-sequence; then select 150Hz protection; its setting value is: ID150Hz=0.85*ID; protect definite value to set a upper limit and a lower limit simultaneously; lower limit is according to detecting that direct current is intermittently determined continuously, and the upper limit is determined according to equipment tolerance.

(5) 150Hz guard time definite value is 0.35 second switched system, and the two poles of the earth adopt the different trip times, and namely one very 3 seconds, another very 6 seconds.

(6) optimizing original 50Hz to protect, if AC second harmonic is positive sequence, determining to protect outside protection or district in district by detecting AC system 2 subharmonic voltage positive sequence component.Determine that employing 3% is as differentiation troubles inside the sample space or the boundary condition of external area error.When AC system 2 subharmonic positive sequence component is less than 3%, adopt protection in district; Adopt when being more than or equal to 3% outside district and protect.

(7) when second harmonic positive sequence component>=3%, 50Hz treats as protecting outside district, and definite value is: ID _50Hz=0.85*ID, protect definite value to set a upper limit and a lower limit, lower limit is according to detecting that direct current is intermittently determined continuously, and the upper limit is according to the harmonic wave tolerance of current conversion station electric equipment simultaneously.

(8) the same with 150Hz, the two poles of the earth adopt different trip time definite value, one very 3 seconds, and another very 6 seconds.

No matter judge according to above-mentioned steps, be that the air-drop of AC transformer is closed a floodgate, or the second harmonic that the situation such as converter valve pulse missing produces, and can judge accurately.Ensure that protection will blindly action cause HVDC to stop transport.

Accompanying drawing explanation

Fig. 1 is the harmonic amplitude that transformer air-drop produces that second harmonic is delivered to DC side generation.In figure, transverse axis is respectively frequency and harmonic number; The longitudinal axis is harmonic amplitude.

Fig. 2 is 100Hz protection amplitude-versus-frequency curve after adjustment.

Fig. 3 is newly-increased 150Hz protection amplitude-versus-frequency curve.

Embodiment

The invention will be further described below: in order to ensure that all impacts of AC second harmonic on direct current system have corresponding protection, and the present invention needs to make specific adjustment to the characteristic of second harmonic and DC side protection.

(1) at current conversion station AC, Characteristics Detection is carried out to second harmonic, especially its positive sequence, negative phase-sequence feature.

(2) original 100Hz protects design parameter as table 1, and its operating current is ID _{100Hz_amp}> 0.2*ID+0.06*ID _nomiD in formula _{100Hz_amp}for direct current harmonic current peak value; ID is actual motion electric current; ID _nomfor rated direct current

Table 1:

Sequence number	Setting value title	Definite value (per unit value/famous value)
			1	100Hz protects alarm setting value	0.04pu/30A
2	100Hz protection starts definite value	0.06pu
			3	100Hz protective ratio rate coefficient	0.2
4	100Hz protection system switching time	0.35s
			5	Power x Time definite value falls in 100Hz protection	2.00s
6	100Hz operate time of protection definite value	3.00s

(3) disturbance of AC positive sequence voltage is in the response of DC side

$U_d^{+}=\underset{m=1}{\overset{\∞}{\mathrm{\Σ}}}\underset{k=0}{\overset{\∞}{\mathrm{\Σ}}}\frac{{3U}_m^{+}}{2}\left\{A_{(6k-1)\mathrm{\α}}\cos \right\{[{\mathrm{\ω}}_m+(6k-1)\mathrm{\ω}]t+a_m^{+}\}+A_{(6k+1)a}\cos \{[{\mathrm{\ω}}_m-(6k-1)\mathrm{\ω}]t+a_m^{+}\left\}\right\}---\left(1\right)$

Similarly, the disturbance of AC negative sequence voltage is in the response of DC side can be expressed as

$U_d^{-}=\underset{m=1}{\overset{\∞}{\mathrm{\Σ}}}\underset{k=0}{\overset{\∞}{\mathrm{\Σ}}}\frac{{3U}_m^{+}}{2}\left\{A_{(6k+1)\mathrm{\α}}\cos \right\{[{\mathrm{\ω}}_m+(6k-1)\mathrm{\ω}]t+a_m^{-}\}+A_{(6k-1)\mathrm{\α}}\cos \{[{\mathrm{\ω}}_m-(6k-1)\mathrm{\ω}]t+a_m^{-}\left\}\right\}$

$U_d^{-}=\underset{m=1}{\overset{\∞}{\mathrm{\Σ}}}\underset{k=0}{\overset{\∞}{\mathrm{\Σ}}}\frac{{3U}_m^{+}}{2}\left\{A_{(6k+1)\mathrm{\α}}\cos \right\{[{\mathrm{\ω}}_m+(6k+1)\mathrm{\ω}]t+{\mathrm{\α}}_m^{-}\}+$

$A_{(6k-1)\mathrm{\α}}\cos \left\{\right[{\mathrm{\ω}}_m-(6k-1)\mathrm{\ω}]t+{\mathrm{\α}}_m^{-}\}\}---\left(2\right)$

From above two formulas, be ω for angular frequency _mpositive sequence disturbance, will ω be produced in DC side _m+ (6k-1) ω and ω _mthe direct current disturbance component of-(6k-1) ω; Same angular frequency is ω _mnegative phase-sequence disturbance will produce ω in DC side _m+ (6k-1) ω and ω _mthe response component of-(6k-1) ω.

In sum, by AC to DC side harmonic voltage close be positive sequence harmonic, number of times subtracts 1; Negative sequence harmonic, number of times adds 1.

(4) 150Hz protection separated from 100Hz protection, namely 100Hz protects Harmonic currents detection bandwidth to be adjusted to 80Hz ~ 120Hz from 80Hz ~ 200Hz, and separately arrange separately 150Hz protection, Harmonic currents detection Bandwidth adjustment is 130Hz ~ 170Hz.Original 100Hz protective current definite value is through Control protection combined debugging verification experimental verification, and suggestion remains unchanged.After time definite value considers direct current one pole fault, another pole power turns generation success, effectively can reduce bipolar probability of simultaneously stopping transport, and therefore the two poles of the earth protection should adopt different trip time, i.e. an extremely first action, another extremely rear action.Bonding apparatus ability and systematic influence, advise that a pole trip time is 3 seconds, another pole trip time is 6s.

(5) if AC second-harmonic detection is negative phase-sequence (transformer air-drop is closed a floodgate and usually produced a large amount of secondary negative sequence component); itself and 100Hz and 150Hz setting value are contrasted; if do not reach operating value, be failure to actuate, accomplish that the division of labor that each is protected is clearly meticulous.

A the setting value of the 150Hz protection after () separation is ID _150Hz=0.85*ID;

B () protects definite value to set a upper limit and a lower limit simultaneously, lower limit is according to detecting that direct current is intermittently determined continuously, and the upper limit is determined according to equipment tolerance.

C () time definite value is 0.35 second switched system, the two poles of the earth adopt the different trip times, and namely one very 3 seconds, another very 6 seconds.The result of 100Hz and 150Hz relay testing is carried out as table 2 for Qinghai-Tibet direct current.

150Hz protection act test when table 2:2 subharmonic negative sequence component 3s is 13.5%, 6s is 12.5%

(6) if detecting AC second harmonic is positive sequence, then contrasting in DC side and 50Hz setting value, determining to protect outside protection or district in district by detecting AC system 2 subharmonic voltage positive sequence component.2 order harmonic components that the 50Hz component that direct current system self loses pulses generation produces in AC system are no more than 1%; adopt in the detection threshold of 3% discriminating district or protect enough reliable outside district; therefore, determine that employing 3% is as differentiation troubles inside the sample space or the boundary condition of external area error.When AC system 2 subharmonic positive sequence component is less than 3%, adopt protection in district; Adopt when being more than or equal to 3% outside district and protect.

A (), when second harmonic positive sequence component >=3%, 50Hz treats as protecting outside district, definite value is: ID _50Hz=0.85*ID, protect definite value to set a upper limit and a lower limit, lower limit is 63.75A, and according to detecting that direct current is intermittently determined continuously, upper limit value is 200A, determines according to capacity of equipment simultaneously;

After the extremely first action of (b), after an other pole power turns generation success, under identical AC system 2 subharmonic positive sequence component condition, rectification side direct current 50Hz component reduces on the contrary, therefore advise that the two poles of the earth adopt different trip time definite value, one very 3 seconds, another very 6 seconds;

C result that () carries out 50Hz relay testing for Qinghai-Tibet direct current is as shown in table 3;

50Hz protection act test when table 3:2 subharmonic positive sequence component 3s is 9%, 6s is 7%

The above is only preferable examples of the present invention, not does any pro forma restriction to the present invention.Any those of ordinary skill in the art, when not departing from technical solution of the present invention scope, the Method and Technology content of above-mentioned announcement can be utilized to make many possible variations and modification to technical scheme of the present invention, or be revised as the Equivalent embodiments of equivalent variations.Therefore, every content not departing from this technological invention scheme, all throw away belong to this technological invention scheme protection range in.

Claims (7)

1. reduce the implementation method that AC system second harmonic causes HVDC to stop transport, it is characterized in that: original 100Hz protection is divided into two protections, and optimize original 50Hz simultaneously and protect.

2. a kind of implementation method reducing AC system second harmonic and cause HVDC to stop transport of base according to claim 1, is characterized in that: change the detection bandwidth that original 100Hz protects, be adjusted to 80Hz ~ 120Hz from 80Hz ~ 200Hz.Original 100Hz protective current definite value is constant, and after time definite value considers direct current one pole fault, another pole power turns generation success; effectively can reduce bipolar probability of simultaneously stopping transport; therefore the two poles of the earth protection should adopt different trip time, i.e. an extremely first action, another extremely rear action.Advise that a pole trip time is 3 seconds, another pole trip time is 6s.

3. a kind of implementation method reducing AC system second harmonic and cause HVDC to stop transport of base according to claim 1, is characterized in that: arrange separately 150Hz protection, Harmonic currents detection Bandwidth adjustment is 130Hz ~ 170Hz.

4. a kind of implementation method reducing AC system second harmonic and cause HVDC to stop transport of base according to claim 1, is characterized in that: the definite value of 150Hz protection is: ID _150Hz=0.85*ID, protect definite value to set a upper limit and a lower limit, lower limit is according to detecting that direct current is intermittently determined continuously, and upper limit value considers the harmonic wave tolerance of current conversion station electric equipment simultaneously.

5. a kind of implementation method reducing AC system second harmonic and cause HVDC to stop transport of base according to claim 1; it is characterized in that: 150Hz guard time definite value is 0.35 second switched system; the two poles of the earth adopt the different trip times, and namely one very 3 seconds, another very 6 seconds.

6. a kind of implementation method reducing AC system second harmonic and cause HVDC to stop transport of base according to claim 1; it is characterized in that: optimize original 50Hz and protect, determining to protect outside protection or district in district by detecting AC system 2 subharmonic voltage positive sequence component.Determine that employing 3% is as differentiation troubles inside the sample space or the boundary condition of external area error.When AC system 2 subharmonic positive sequence component is less than 3%, adopt protection in district; Adopt when being more than or equal to 3% outside district and protect.

7. a kind of implementation method reducing AC system second harmonic and cause HVDC to stop transport of base according to claim 1, is characterized in that: when second harmonic positive sequence component>=3%, 50Hz treats as protecting outside district, and definite value is: ID _50Hz=0.85*ID, protect definite value to set a upper limit and a lower limit, lower limit is according to detecting that direct current is intermittently determined continuously, and the upper limit considers the harmonic wave tolerance of current conversion station electric equipment simultaneously.