SE425994B

SE425994B - Equipment for high-voltage testing

Info

Publication number: SE425994B
Application number: SE8102888A
Authority: SE
Inventors: B Grundmark
Original assignee: Asea Ab
Priority date: 1981-05-08
Filing date: 1981-05-08
Publication date: 1982-11-29
Also published as: SE8102888L

Abstract

Equipment for high-voltage testing of primarily capacitive test objects contains a high-voltage inductor 1 which together with the test object 4 is part of a series resonance circuit. The circuit is energised by a load-switched static converter 2. The static converter is connected in parallel with an auxiliary capacitor 3 connected in series with the inductor 1 and the test object 4 in the resonance circuit, whose capacitance is substantially larger than the capacitance of the test object 4. <IMAGE>

Description

_15 20 25 šO 8102888-s 2 man därvid i resonanskretsen använda reaktor-element med fasta induk- tansvärden och mata kretsen från en spänningskälla med kontinuerligt variabel frekvens. Vid en tidigare föreslagen sådan utrustning använ- des en serieresonanskrets som seriematas från en frekvensomriktare. 8102888-s 2 reactor elements with fixed inductance values are used in the resonant circuit and the circuit is supplied from a voltage source with a continuously variable frequency. In a previously proposed such equipment, a series resonant circuit was used which is fed in series from a frequency converter.

Därvid uppnås väsentliga fördelar genom att man undviker den mekaniskt reglerbara reaktorn och får endast statiska apparater i huvudkretsarna. Ändamålet med föreliggande uppfinning är att vidareutveckla och förenkla den sistnämnda typen av provutrustning. Detta uppnås genom den i känneteck- nande delen av patentlcrav 1 eller 2 angivna åtgärden, vilken gör det möjligt att använda en enklare omriktare än vid den tidigare föreslagna utrustningen.Significant advantages are achieved by avoiding the mechanically controllable reactor and only having static devices in the main circuits. The object of the present invention is to further develop and simplify the latter type of test equipment. This is achieved by the measure specified in the characterizing part of claim 1 or 2, which makes it possible to use a simpler converter than with the previously proposed equipment.

Uppfinningen bygger på. insikten om att den enklaste och mest okritiska typen av strömriktare med variabel frekvens arbetar som en ströminjektor, varför den måste kopplas till resonanskretsen i parallell, inte i serie såsom strömmar-en vid den kända utrustningen. Ä andra sidan är det fördelaktigt att vid resonansprovkretsar för högspänning använda seriematning, eftersom detta reducerar storleken av den nödvändiga matningstransformatorn, som skall tillföra erforderlig energi för att täcka förlusterna i lmetsen. Provlcxretsarna har deek vanligen ett nweket högt gednetecal (o-värde), den detta mömggör att man genom att anordna en hjälpkondensator såsom anges i patentkrav 1 eller 2 kan eliminera kontroversen mellan ovannämnda önskemål.The invention is based on. the realization that the simplest and most uncritical type of variable frequency converter operates as a current injector, so it must be connected to the resonant circuit in parallel, not in series as the current in the known equipment. On the other hand, it is advantageous to use series supply in high voltage resonant test circuits, as this reduces the size of the necessary supply transformer, which must supply the necessary energy to cover the losses in the melt. The test circuits usually have a slightly high gednetecal (o-value), which makes it possible that by arranging an auxiliary capacitor as stated in claim 1 or 2, the controversy between the above-mentioned wishes can be eliminated.

Uppfinningen skall förklaras närmare genom beskrivning av utföringsexempel under hänvisning till bifogade ritning, i vilken fig 1 visar principen för en enligt uppfizmingen utförd utrustning för hög- spänningsprovning, medan fig 2 och 3 visar kopplingar för två. praktiska utföringsformer av en sådan utrustning. i Fig 1 visar principen för en enligt uppfinningen utförd utrustning för hög- spänningsprovning av huvudsakligen kapacitiva provobjekt såsom exempelvis isoleringen i SF6-gasisolerade ställverk. Utrustningen omfattar en hög-spän- ningsrealctor 1, en spänningskälla 2 med kontinuerligt varierbar frekvens samt en över spänningskällans utgångsklänmor ansluten hjälpkondensator 3. Prov- objektet beteclcxxes med 4.The invention will be explained in more detail by describing exemplary embodiments with reference to the accompanying drawing, in which Fig. 1 shows the principle of a high-voltage test equipment according to the invention, while Figs. 2 and 3 show connections for two. practical embodiments of such equipment. Fig. 1 shows the principle of an equipment according to the invention for high-voltage testing of mainly capacitive test objects such as, for example, the insulation in SF6 gas-insulated switchgear. The equipment comprises a high-voltage reactor 1, a voltage source 2 with continuously variable frequency and an auxiliary capacitor 3 connected across the output terminals of the voltage source. The test object is rated with 4.

Spänningskällan 2 utgöres av en lastkommuterad strömriktare, vilken ger en 10 15 20 25 SO 8102888-8 växelström i form av fyrkantpulaer med en frekvens som bestäms av belast- ningen. Denna strömriktare kan lämpligen vara utförd som en frekvensomrik- tare med likströmsmellaziled och omfatta en lilmiktardel 5 och en växel- riktardel 6, såsom visas i fig 2 och 3. I detta fall matas strömriktaren med trefasig spänning från ett lågspäxmingsnät 7, och mellan likriktardelen och växelriktardelen anordnas på konventionellt sätt en glättniligsreaktor.The voltage source 2 consists of a load-commutated converter, which provides an alternating current in the form of square pulses with a frequency determined by the load. This converter can suitably be designed as a frequency converter with DC intermediate line and comprise a rectifier part 5 and an inverter part 6, as shown in Figs. 2 and 3. In this case the converter is supplied with three-phase voltage from a low voltage network 7, and between the rectifier part and the inverter part is arranged in a conventional manner with a smoothing reactor.

En för föreliggande ändamål lämplig frekvensomriktare av detta slag 'air när- mare beskriven i ASEA Tidning 1973, h 5, s 105-112. Strömriktaren kan i princip även utgöras av en från ett batteri matad växelrilctare.A frequency converter of this type suitable for the present purpose is described in more detail in ASEA Tidning 1973, h 5, pp. 105-112. The converter can in principle also consist of an inverter supplied from a battery.

Högspänningsreaktorn 1 bildar tillsammans med provobjektet 4 och hjälpkon- densatom 5 en serieresonanslcrets. 'Kretsens resonansfrekvens är 04-01 1 °1 |I Lc där L -= reaktorns (1) induktans C = provobjektets (4) kapaoitans G1 = hjälpkondensatoms (5) kapaoitans Om lmetsen tillförs en energipuls, vilket sker med hjälp av en ej visad startkrets, komer en svängning med ovan angivna frekvens att uppstå mellan kretsens kapacitans och induktans. Med hjälp av ett till s etsen anslutet styrpulsdon lämnas styrpulser till växelriktarens tyristorer i takt med svänglingen i lcretsen. Provlcretsen tillförs därvid via strömriktaren en energi som täcker förlusterna i provlcretsen, varvid svängningen hålls vid liv.The high voltage reactor 1 together with the test object 4 and the auxiliary capacitor 5 form a series resonant circuit. The resonant frequency of the circuit is 04-01 1 ° 1 | I Lc where L - = inductance of the reactor (1) C = capacitance of the sample object (4) G1 = capacitance of the auxiliary capacitor (5) If the energy is applied to an pulse, starting circuit, an oscillation with the above frequency will occur between the capacitance of the circuit and the inductance. With the aid of a control pulse device connected to the weld, control pulses are supplied to the thyristors of the inverter in step with the oscillation in the circuit. The test circuit is then supplied via the converter with an energy which covers the losses in the test circuit, whereby the oscillation is kept alive.

Strömriktaren 2 är spänningsreglerad, dvs utspänningen hålls vid inställt värde oavsett belastníngsvariationer, förutsatt att strömmen ej blir så hög att en genom en inbyggd begränsningsanordning bestämd strömgräns uppnås.The converter 2 is voltage-regulated, ie the output voltage is kept at the set value regardless of load variations, provided that the current does not become so high that a current limit determined by a built-in limiting device is reached.

Spänningsinställxiingen görs med en potentiometer.The voltage setting is done with a potentiometer.

Eftersom Q-värdet för de här ifrågavarande provlcretsarna är relativt högt (exempelvis 50), och G1 är väsentligt större än C (exempelvis G1 = 10 C) blir spänningen UG över provobjektet vid resonansfrekvensen många. gånger större än kretsens matningsspännjng Uh. Provspäxzníngen Uc kan uttryckas som funktion. av den från strömriktaren tillfördaströmmen Ia på följande sätt: Ue“Ia'__ö°_'°'Since the Q value of the test circuits in question is relatively high (for example 50), and G1 is significantly larger than C (for example G1 = 10 C), the voltage UG across the test object at the resonant frequency becomes many. times greater than the supply voltage of the circuit Uh. The test specimen Uc can be expressed as a function. of the current Ia supplied from the inverter as follows: Ue “Ia '__ ö ° _' ° '

Claims

10 15 20 8102888-8 / ï ° >> 1 ﬁ äfqf? wherein r denotes the resistance of the test circuit, which is relatively small. The current I a supplied from the converter is in the form of a square wave which contains odd harmonics. However, due to the high quality number Q of the circuit, the harmonics will not have a significant effect. the sinusoidal shape of the specimen. The converter 2, which is usually supplied from a low-voltage network, provides an alternating voltage of up to, for example, 600 V. The test circuits must be designed for 1000-3000 kVA and for test voltages up to 500-800 kv, the input to the resonant circuit itself must be of the order of magnitude 20-100 kV. This means that in practice a transformer must be arranged between the converter and the resonant circuit. Figures 2 and 5 show two. different connections with such an intermediate transformer 6. In the embodiment according to Fig. 2, the crane transformer is loaded only with the loss power of the test circuit, which only amounts to 1-2% of the reactive test power. In the embodiment according to Fig. 5, the transformer is also loaded with the reactive power of the auxiliary capacitor 3 ', which can amount to 10-20 7: of the total test power. This connection therefore requires a slightly more expensive transformer than the connection according to Fig. 2. An advantage of the connection according to Fig. 5, however, is that the auxiliary capacitor 3 'is of low voltage design, whereby it is more possible to vary the capacitance by connecting a larger or smaller number of capacitor units. Thereby it can be achieved that the variations in the test frequency when testing test objects with different capacitances become smaller. PATEKWTIQYAV i

1.. Equipment for high-voltage testing of mainly capacitive sample-x objects, which equipment comprises a high-voltage reactor (1), which together with the test object (4) is included in a resonant circuit, and a converter (2) for alternating current supply of the resonant excitation, characterized therefrom, that the converter (2) is load-commutated and connected in parallel with an auxiliary capacitor (3) connected in the resonant charge in series with the reactor (1) and the test object (4), whose capacitance (01) is substantially greater than the capacitance (C) at the sample object 8102888-8

2. Equipment for high voltage testing of mainly capacitive. test object, which equipment comprises a high-voltage reactor (1), which together with the test object (4) is included in a resonant circuit, and a load-switched converter (2) for alternating current supply of the resonant circuit, characterized in that the converter (2) is connected in parallel with an auxiliary capacitor (5 l), which is connected to a low-voltage primary winding of a transformer (8), the high-voltage secondary winding of which is connected in series with the reactor (1) and the sample beam (4), wherein the over-transformed capacitance of the auxiliary capacitor (3 ') to the secondary side of the transformer is significantly greater than that of the test object.

Equipment according to claim 1 or 2, characterized in that the high-voltage oxidation reactor (1) comprises one or more reactor elements with fixed inductance values.

Equipment according to claim 1, 2 or 3, k "a". n n e t e c k n a d of the fact that the converter (2) consists of a frequency converter containing a controlled rectifier (5), which feeds an inverter (6) via a smoothing reactor.

5. Equipment according to any one of the preceding claims, characterized in that the converter (2) comprises a starting circuit arranged to set the resonant terminal (1, 5, 4) in oscillation.