Технические науки/5. Энергетика

Candidate of Science N.L. Batseva, student A.P. Shubenkina

Tomsk Polytechnic University, Russia

The flux transfer in advanced

Tomsk interconnected power network

In Tomsk power system (PS) consumers are provided electrical energy by 220kV double-circuit overhead line which begins on Nizhnevartovsk Power Plant (PP) (Tyumen PS), passes via seven substations of Tomsk PS: Sovietsko-Sosninskaya – Chapaevka – Raskino – Vertikos – Parabel – Chazhemto – Volodino and ends on Tomskaya substation (further Nizhnevartovsk PP – Tomskaya). The length of this line is 800 km, and nowadays it is operating as no-load line between substations Vertikos and Parabel (figure 1).

Figure 1 – The fragment of Tomsk interconnected power network with no-load line

This fact leads to the power supply deterioration of oil and gas industry consumers (single-way feed from Tyumen PS); unacceptable boosting or reduction of the voltage value on the long-distance substation busbars.

Unfortunately it is impossible to improve the power supply reliability by using Vertikos – Parabel line as the double-way feed line because of current overload in the main line Nizhnevartovsk PP (Tyumen PS) – Sovietsko-Sosninskaya under conditions of emergency or maintenance on one circuit the last (table 1).

Table 1 – Results of regime calculation under condition when Vertikos – Parabel line is switched on two ends

Name of overhead line	Wire mark	Admissible continuous current I, А (outdoor)	State of operation	Current, A
Nizhnevartovsk PP – Sovietsko-Sosninskaya	АS 240/32	610	Two circuits are in service	346
			One circuit is switched off	611

One of ways to redress situation is development of interconnected network by means of place into service 500kV single-circuit overhead line Nizhnevartovsk PP – Tomskaya till 2016 [1]. In practice, it corresponds the case when 220kV overhead line will operate with 500 kV overhead line in parallel.

According to the results (table 2), under the condition of inherent power flowing via 220 kV and 500 kV overhead lines, the desired effect of improving power transmission capacity is not observed: 500kV overhead line is underused but 220kV overhead line operates under power transmission capacity limit, which leads to the magnifying of total power and energy losses.

Table 2 – Power flows under the condition of inherent power flowing

Name of overhead line	Overhead line voltage, kV	Power flow
		P, MW	Q, Mvar
Sovietsko-Sosninskaya – Chapaevka	220	232	128
Sovietsko-Sosninskaya – Parabel	500	50	185

It is possible to redistribute power flows between 220kV and 500kV overhead lines correctly by using of the phase shifter device (PSD) installed on Sovietsko-Sosninskaya substation. Technical characteristics of PSD are presented in table 3.

Table 3 – Technical characteristics of PSD

Name of parameter	Parameter value
Capacity, MWA	226
Permissible current in OL, A	787
Phase shift (angle) of voltage, electrical degree	±40
Number of ratio steps	±15
Ratio step, electrical degree	2,67
Time of phase shift (angle) changing (no more), s	0,02

Generally, the PSD consists of two transformers: regulated T1 and series T2, which produces the additional voltage vector, directed to the voltage vector at the beginning of the overhead line perpendicularly and forms the phase shift relatively to the main voltage (figure 2).

Figure 2 – The scheme of PSD

Under varying of voltage on series winding by regulated transformer, the vector rotation of total voltage at the beginning of an overhead line is accomplished. Consequently, under changing of a power flow, transmitted through the line, controlling a voltage phase at the beginning and in the end of the line is possible [2].

The regime calculation of interconnected network with PSD installed on Sovietsko-Sosninskaya substation has been done by means of RastrKZ software. Phase shifter device is modeled by including CT ratio: К_Т/r, К_Т/i – the real and imaginary components of CT ratio (figure 3).

Figure 3 – Modeling of PSD in RastrKZ software

CT ratio is determined by formula (1):

₍₁₎

where δ – is the shift angle between vectors of voltage, electrical degree.

Originally, the resistance of PSD branch is assumed to be zero, that is corresponded the CT ratio equals 0.99 ± j0.046.

Under changing the value of CT ratio, power flows are forcibly redistributed from 220 kV to 500 kV to optimal values (table 4).

Table 4 – The flux transfer by means of PSD

Phase shift angle between voltage vectors	Total power losses, MVA	Power flows, MVA
		Sovietsko-Sosninskaya–Chapaevka (220 kV)	Nizhnevartovsk PP–Sovietsko-Sosninskaya (220 kV) (by two circuits)	Sovietsko-Sosninskaya–Parabel (500 kV)
0 (phase shifter device does not operate)	54,1+j635	98-j14	230-j128	-50+j136
+2,67	53,5+j633	78-j4	220-j122	-60+j139
+5,34	53,3+j632	56+j0,1	208-j118	-71+j140
+10,68	54+j635	16+j14	188-j106	-92+j141
+16,02	56,5+j646	-24+j28	168-j92	-112+j141
+21,36	60,6+j664	-62+j44	76-j78	-132+j140
+24,03	63,4+j676	-80+j52	142-j62	-142+j139
+32,04	74+j722	-132+j80	120-j22	-170+j136
+37,38	82,9+j762	-164+j58	108+j10	-187+j133
+40,00	87,7+j782	-178+j104	104+j26	-195+j131

Based on these results, it is concluded that the PSD optimal switching angle is approximately 11 electrical degrees. Under this angle 220kV power lines will detrain but 500kV power line will load while total power losses will identical with the case when PSD does not operate.

References

1. About scheme and program of Tomsk power system future development for the period 2013-2017 [Official site of Tomsk region Administration]. URL: docs.pravo.ru/document/view/26481664/26384921 (date of circulation 17.08.2013).

2. Stelmakov V.N. Phase shifter device with thyristor adjustment // Electricity.-2010.-№8.-P. 20-23.