Overexcitation protection function block description

Transcription

1 unction block description Document ID: PRELIMIARY VERSIO

2 ser s manual version inormation Version Date Modiication Compiled by Preliminary Preliminary version, without technical inormation Petri PRELIMIARY VERSIO 2/15

3 COTETS 1 Overexcitation protection unction Application Mode o operation Calculation o the lux Starting o the unction Operating characteristics Deinite time characteristic IEEE standard dependent time characteristics Analogue input o the unction Structure o the overexcitation protection algorithm The lux calculation (lux calculation) The deinite time and the inverse type characteristic (Characteristics ) The decision logic (Decision logic) Technical summary Technical data The parameters Binary output status signals The binary input status signals The unction block The requency range The voltage range The lux range PRELIMIARY VERSIO 3/15

4 1 Overexcitation protection unction 1.1 Application The overexcitation protection unction is applied to protect generators and unit transormers against high lux values causing saturation o the iron cores and consequently high magnetizing currents. The problem to be solved is as ollows: The lux is the integrated value o the voltage: ( t) t 0 u( t dt 0 ) In steady state, this integral can be high i the area under the sinusoidal voltage-time unction is large. Mathematically this means that in steady state the lux, as the integral o the sinusoidal voltage unction, can be expressed as ( t) k The peak value o the lux increases i the magnitude o the voltage increases, and/or the lux can be high i the duration o a period increases; this means that the requency o the voltage decreases. That is, the lux is proportional to the peak value o the voltage (or to the RMS value) and inversely proportional to the requency. ote: the overexcitation protection unction is intended to be applied near the generator, where the voltage is expected to be pure sinusoidal, without any distortion. Thereore, a continuous integration o the voltage and a simple peak detection algorithm can be applied. The eect o high lux values is the symmetrical saturation o the iron core o the generator or that o the unit transormer. During saturation, the magnetizing current is high and distorted; high current peaks can be detected. The odd harmonic components o the current are o high magnitude and the RMS value o the current also increases. The high peak values generate high dynamic orces, the high RMS value causes overheating. During saturation, the lux leaves the iron core and high eddy currents are generated in the metallic part o the generator or transormer in which normally no current lows, and which is not designed to withstand overheating. The requency can deviate rom the rated network requency during start-up o the generator or at an unwanted disconnection o the load. In this case the generator is not connected to the network and the requency is not kept at a constant value. I the generator is excited in this state and the requency is below the rated value, then the lux may increase above the tolerated value. Similar problems may occur in distributed generating stations in case o island operation. The overexcitation protection is designed to prevent this long-term overexcited state. cos t PRELIMIARY VERSIO 4/15

5 1.2 Mode o operation Calculation o the lux The lux is calculated continuously as the integral o the voltage. In case o the supposed sinusoidal voltage, the shape o the integrated lux will be sinusoidal too, the requency o which is identical with that o the voltage. The magnitude o the lux can be ound by searching or the maximum and the minimum values o the sinusoid Starting o the unction The magnitude can be calculated i at least one positive and one negative peak value have been ound, and the calculated lux magnitude is above the setting value. Accordingly, the starting delay o the unction depends on the requency: i the requency is low, more time is needed to reach the opposite peak value. In case o energizing, the time to ind the irst peak depends on the starting phase angle o the sinusoidal lux. I the voltage is increased continuously by increasing the excitation o the generator, this time delay cannot be measured Operating characteristics The most harmul eect o the overexcited state is unwanted overheating. As the heating eect o the distorted current is not directly proportional to the lux value, the applied characteristic is o inverse type (so called IEEE type): I the overexcitation increases, the operating time decreases. To meet the requirements o application, a deinite-time characteristic is also oered in this protection unction as an alternative. The supervised quantity is the calculated / value as a percentage o the nominal values (index ): G 100[%] 100[%] The over-dimensioning o generators in this respect is usually about 5%, that o the transormer about 10%, but or unit transormers this actor can be even higher. At start-up, the protection unction generates a warning signal aimed to inorm the controller to decrease the excitation, and generates a trip signal to decrease or to switch o the excitation and the generator. I the time determined by the parameter values o the selected characteristics expires, the unction generates a trip command. PRELIMIARY VERSIO 5/15

6 Deinite time characteristic Operating time t G) ( when G GS t OP t(g) t OP G G S Figure 1-1 Overexcitation independent time characteristic where t OP (seconds) G G S theoretical operating time i G> G S, ix, according to the parameter setting (VPH24_MinDel_TPar_, Min. Time Delay). measured value o the characteristic quantity; this is the value as a percentage o the rated value. peak setting value o the characteristic quantity (VPH24_EmaxCont_IPar, Start / lowset). This is the rated value. set set peak value as a percentage o the Reset time where t Drop-o (seconds) t G) G 0.95*G ( t Drop o when S drop-o time i G< 0.95*G S, ix, value. PRELIMIARY VERSIO 6/15

7 IEEE standard dependent time characteristics Operating time IEEE square law t 0.18* TMS V/ Vset / ( V / V / set ) * TMS 2 (G G ) S Where TMS = 1-60, V/ V / V set / set time multiplier setting, lux value calculated at the measured voltage and requency, lux at rated voltage and rated requency, lux setting value. t/tms VPH24_MaxDel_TPar_ (Max.Time Delay) /TMS (V/)/(Vset/set) Figure 1-2 IEEE standard dependent time characteristics The maximum delay time is limited by the parameter VPH24_MaxDel_TPar_ (Max.Time Delay). This time delay is valid i the lux is above the preset value VPH24_EmaxCont_IPar_ (Start / lowest). PRELIMIARY VERSIO 7/15

8 t/tms 0,6 0,5 0,4 0,3 0,2 0,1 VPH24_MinDel_TPar_ (Min.Time Delay) /TMS (V/)/(Vset/set) Figure 1-3 IEEE standard dependent time characteristics (enlarged) This inverse type characteristic is also combined with a minimum time delay, the value o which is set by user parameter VPH24_MinDel_TPar_ (Min. Time Delay). This time delay is valid i the lux is above the setting value VPH24_Emax_IPar_ (Start / highset). Reset time I the calculated lux is below the drop-o lux value (when G.95*G 0 ), then the calculated lux value decreases linearly to zero. The time to reach zero is deined by the parameter VPH24_CoolDel_TPar_ (Cooling Time). S Analogue input o the unction Overexcitation is a typically symmetrical phenomenon. There are other dedicated protection unctions against asymmetry. Accordingly, the processing o a single voltage is suicient. In an isolated network, the phase voltage is not exactly deined due to the uncertain zero sequence voltage components. Thereore, line-to-line voltages are calculated based on the measured phase voltages, and one o them is assigned to overluxing protection. As overexcitation is a phenomenon which is typical i the generator or the generator transormer unit is not connected to the network, the voltage drop does not need any compensation. I the voltage is measured at the supply side o the unit transormer, then the voltage is higher then the voltage o the magnetization branch o the transormer s equivalent circuit. Thus the calculated lux cannot be less then the real lux value. The protection operates with increased security. PRELIMIARY VERSIO 8/15

9 1.3 Structure o the overexcitation protection algorithm Fig.1-4 shows the structure o the overexcitation protection (VPH24) algorithm. VPH24 LL Flux integration Characteristics Decision Logic Status signals Parameters Status signals Figure 1-4 Structure o the overexcitation protection algorithm The inputs are the sampled values o a line-to-line voltage (LL), parameters, status signals. The outputs are the binary output status signals. The sotware modules o the overexcitation protection unction: Flux calculation This module integrates the voltage to obtain the lux time-unction and determines the magnitude o the lux. Characteristics This module calculates the required time delay based on the magnitude o the lux and the parameter settings. Decision logic The decision logic module combines the status signals to generate the trip command o the unction. The ollowing description explains the details o the individual components. PRELIMIARY VERSIO 9/15

10 1.4 The lux calculation (lux calculation) This module integrates the voltage to obtain the lux time-unction and determines the magnitude o the lux. LL Flux calculation FluxMagn Figure 1-5 Principal scheme o the lux calculation The inputs are the sampled values o a line-to-line voltage (LL). The output is the magnitude o the lux (FluxMagn), internal signal. PRELIMIARY VERSIO 10/15

11 1.5 The deinite time and the inverse type characteristic (Characteristics ) This module calculates the required time delay based on the magnitude o the lux and the parameter settings. The inputs are the magnitude o the lux (FluxMagn) and parameters. The outputs are the internal status signals o the unction. These indicate the started state and the generated trip command i the time delay determined by the characteristics expired. FluxMagn Binary outputs Parameters Characteristics Figure 1-6 Schema o the characteristic calculation Enumerated parameter Parameter name Title Selection range Deault Parameter or type selection Deinite VPH24_Oper_EPar_ Operation O,DeinitTime,IEEE Time Table 1-1 The enumerated parameter o the overexcitation protection unction Integer parameter Parameter name Title nit Min Max Step Deault Setting value o the overexcitation protection unction VPH24_EmaxCont_IPar_ Start / lowset % Flux value above which the IEEE inverse type characteristic is replaced by the declared minimum time VPH24_Emax_IPar_ Start / highset % Table 1-2 The integer parameters o the overexcitation protection unction PRELIMIARY VERSIO 11/15

12 Timer parameter Parameter name Title nit Min Max Step Deault Minimal time delay or the inverse characteristics and delay or the deinite time characteristics: VPH24_MinDel_TPar_ Min. Time Delay* msec Minimal time delay or the inverse characteristics: VPH24_MaxDel_TPar_ Max. Time Delay* msec Reset time delay or the inverse characteristics: VPH24_CoolDel_TPar_ Cooling Time * msec Time multiplier or the inverse characteristics: VPH24_k_TPar_ Time Multiplier* msec Table 1-3 Timer parameters o the overexcitation protection unction PRELIMIARY VERSIO 12/15

13 1.6 The decision logic (Decision logic) The decision logic module combines the status signals, binary and enumerated parameters to generate the trip command o the unction. VPH24_St_GrI_ AD VPH24_GenSt_GrI _ VPH24_Tr_GrI_ AD VPH24_GenTr_GrI _ VPH24_Blk_GrO_ OT Figure 1-7 The logic scheme o the overexcitation protection unction Binary status signals The overexcitation protection unction has a binary input signal, which serves the purpose o disabling the unction. The conditions o disabling are deined by the user, applying the graphic equation editor. Binary status signal VPH24_Blk_GrO_ Explanation Output status o a graphic equation deined by the user to disable the overexcitation protection unction. Table 1-4 The binary input signal o the overexcitation protection unction The binary output status signals o the overexcitation protection unction are listed in Table 1-5. Binary output signals Signal title Explanation VPH24_GenSt_GrI_ General Start Starting o the unction VPH24_GenTr_GrI_ General Trip Trip command o the unction Table 1-5 The binary output status signals o the overexcitation protection unction PRELIMIARY VERSIO 13/15

14 1.7 Technical summary Technical data Function Eective range* Accuracy* Operating characteristic Reset ratio Operate time Reset time *To be deined by types tests Table 1-6 Technical data o the overexcitation protection unction The parameters The parameters are summarized in Chapter Binary output status signals The binary output status signals o the overexcitation protection unction are listed in Table 1-7. Binary output signals Signal title Explanation VPH24_GenSt_GrI_ General Start General starting o the unction VPH24_GenTr_GrI_ General Trip General trip command o the unction Table 1-7 The binary output status signals o the overexcitation protection unction The binary input status signals Binary input signals The overexcitation protection unction has a binary input signal, which serves the purpose o disabling the unction. The conditions o disabling are deined by the user, applying the graphic equation editor. Binary input signal VPH24_Blk_GrO_ Explanation Output status o a graphic equation deined by the user to disable the overexcitation protection unction. Table 1-8 The binary input signal o the overexcitation protection unction PRELIMIARY VERSIO 14/15

15 1.7.5 The unction block The unction block o the overexcitation protection unction is shown in Figure 1-8. This block shows the binary input status signal, which serves the purpose o triggering the record. It is deined by the user in the graphic equation editor. Figure 1-8 The unction block o the overexcitation protection unction The requency range The eective requency range includes all requencies where the deined accuracy can be achieved. I the requency is too small, then the time needed to ind the peak values and to calculate the lux increases. In contrast, at high requencies the accuracy o the detected peak value decreases. The requency range monitored extends rom 10 Hz to 70 Hz. The details are given among the technical data The voltage range Similarly to the requency range, the voltage range is also limited. I the voltage is too small, the voltage measurement becomes inaccurate due to the sampling. In case o high voltage at low requencies, in addition to the generator and the unit transormer, the voltage transormers may also saturate. Accordingly, the requency range and the voltage range are closely related. The voltage range monitored extends rom 10 V to 170 V. The details are given among the technical data The lux range The lux range is the combination o the voltage range and the requency range. For overluxing protection, the eective lux range extends rom 0.5 to 1.5 /. PRELIMIARY VERSIO 15/15