Abstract - Master of DonNTU Vasyliev Viacheslav - Rated short-circuit currents in the system of their own needs 6 kV power of 200 MW SbTES n connection with the installation of unit 4 of the CFB boiler and the changes equipment parameters of their own needs

At power station. № 4 Starobeshevsko TPS performed a replacement coal – fired boiler in the boiler type CFB – 670. This resulted in a change in the scheme and the composition of aggregates sn at voltages as 6 kV and 0.4 kV. In addition to SbTES SRTON been replaced with more powerful (40 MVA). Changing the power scheme and equipment have led to an increase in the currents and circuit complexity modes of equipment and conductors. For the first time calculations of short circuit currents due to the reconstruction unit Art. № 4 SbTES were performed by the project developer, the reconstruction unit "Mgengineering Lurgi Lentjes" and received short-circuit currents 31.187 kA at "worst case" operation. After the guide SbTES instructed to perform the calculations self-electric mode and short circuit currents Donetsk Planning Institute Teploelektroproekt. In this paper, short – circuit current values proposed to define the methods of mathematical modeling of the main circuit wiring and electrical system sc with the use of computers. to improve the reliability of the electrical part SbTES.

Made on SbTES major changes to the scheme of electrical connections and systems sn led to a change in the short-circuit currents that caused the need for testing of electrical equipment and conductors in the first place of the fourth power.

The aim of research is the calculation of short circuit currents in the sc Thermal power plants using the methods of mathematical modeling with PC-based matrix methods for calculating multi-node electrical circuits. Checking equipment and conductors under the terms of these currents.

Wiring SbTES the voltage 6 — 220 kV, Fig. 1, has a large number of branches (over 300), knots (over 200) and short-circuit calculation points (over 100).

Figure 1. equivalent circuit SBTES (animation consists of 7 shots with a delay of 80 ms between frames, the number of cycles of reproduction is limited to 5 th)

Due to the fact that the sections of sc 6 kV power can draw power from three or four sources (SbTES it own workers and TON SRTON 301T and 302T), calculations short circuit currents were separated into two phases. First, calculations were made in the scheme of the main electrical connections to determine the issue of the most powerful sources of supply sections sn from the main circuit. Then, short-circuit currents were calculated for the actual sections sn to select the maximum source and taking into account the makeup of the electric motors [1]. In this paper, the method of nodal potentials in the vector-matrix form. His basic equation has the form

where Uu – the vector of unknown node voltages; Yu – a square matrix of nodal conductivities; Iu – vector of nodal currents. Accounting resistances of all branches of the settlement scheme will automate the finding of the decay time constant of the aperiodic component short-circuit currents, and based on these values of shock circuit currents, thermal pulse, etc [4].

To automate the initial formation of the matrix and vector Yu Iu used auxiliary matrix description of the branches of V. Each row of this matrix for a separate branch of the computational scheme consistently recorded:

– Symbols branches;

– Symbols node from which the output current branch;

– The same, but for the current branch, which enters the node;

– Impedance branches;

– Emf active branch (of the system, generators, IM).

As in the electric circuit SbTES there are several voltage steps (220, 110, 35 and 6 kV), the calculations of short circuit currents for SGES performed [5].

The results of the calculation of short circuit currents from the system and the generators in the system and SGES sn 6 kV

Calculations of short circuit currents were performed on a PC program calculation. Initially, we calculated the short circuit currents for SGES and the system working and backup power sc 6 kV SbTES without recharge from the IM.
The results of the calculation of the total initial value of periodic component short – circuit currents from all sources of energy (power systems and generators) (except for make – up of IM), as well as the magnitude of maximum heat – pulse circuit currents for the sections of sc 6 kV station, the first stage, sections o.n. All units SbTES, as well as new sections of the boiler with CFB shown in Table 1.

Table 1. Total value of current and heat-pulse circuit on the sections o.n. units

Place CS	The source and magnitude of CS
Place CS	current from TON, кА	current from SRTON, кА	peak instantaneous , кА	heat pulse overcurrent fault CS, кА2 с
o.n. the first stage of PS
for 20Т		15,56	40,0	53,15
for 21Т
existing o.n. power (powered by 301T)
4А	13,5	19,3	50,9	88,7
5А	13,2	18,5	48,75	81,3
6А	13,5	17,8	46,8	74,8
7А	-	17,1	45,0	71,0
8А	15,5	16,5	43,3	63,9
9А	16,0	15,75	41,3	55,9
existing o.n. power (powered by 302T)
10А	13,4	16,5	43,6	65,6
11А	13,4	17,1	45,3	71,0
12А	13,75	17,8	47,1	77,1
13А	13,6	18,5		84,0
New section boiler with CBB
4BBA		18,75	49,1	56,9
4BBB		18,74	49,0	56,7

As seen from Table. 1 in most cases (except Block Art. № 9) short – circuit current of the system from backup sources exceeds the fault current from the working sources. Thus, the maximum short-circuit currents from the system were selected as the basic for further calculations. According to this maximum short circuit currents in the same table (see Table 1) were calculated shock instant short-circuit currents and their thermal pulses for the calculation of thermal equipment and conductors

The results of the testing equipment and conductors of their own needs

The total value of short circuit currents and their components consist of a short circuit currents from the system and generators and fault current makeup of the IM. The summation of individual components carry short circuit currents [2].

2.1. Breaking capacity of circuit breakers 6 kV switchgear cells

These test circuit breaking capacity of cells CRU system o.n. 6 kV are shown in Table 2.

Table 2. The results of the test cell switches switchgear feeders o.n. 6 kV power station. № 4 – 13

Section o.n. 6 кV	periodic component			aperiodic component
Section o.n. 6 кV	I_{nt rasch}кА	I_otklкА	i_pr%	i_{аt rasch}кА	BI_otkl,кА	i_pr,%
4 А 5 Б 6 Б 8 Б 9 Б 10 Б 11 Б 12 Б 13 Б	23,96 20,7 20 18,6 18,2 18,9 19,2 20,05 20,5	31,5 20 20 20 20 20 20 20 20	- 3,5 - - - - - 0,25 2,5	14,8 6 5,7 5,1 3,1 5,97 6,2 6,6 6,9	10,1 1,74 1,74 1,74 1,74 1,74 1,74 1,74 1,74	-- 14.7 10.5 2,1 -- 6,5 8.5 13.7 16.7
1 Phase	15,6	20	-	2,3	1,74	--

As seen from Table. 2, the breaking capacity of circuit breakers switchgear feeder cells o.n. 6 kV power and o.n. Phase 1 stations (except for cells o.n. 4 power and o.n. 1 queue TPP) are either limiting value, or exceed it (to a maximum of 16,7%).

2.2. Dynamic stability of cells 6 kV switchgear

Verification data on the dynamic stability of switchgear cells shown in Table 3.

Table 3. The results of the test cell switches switchgear feeders o.n. 6 kV power and sn Phase 1 TES

Section o.n. 6 кV	4 А	5 Б	6 Б	8 Б	9 Б	10 Б	11 Б	12 Б	13 Б	o.n.1 – st stage
i_sp,кА	76,4	73,1	71,4	67,2	64,9	69,9	69	72,4	70,9	40
i_add	82	52	52	52	52	52	52	52	52	52
%	-	40,6	37,7	29	24,8	34,4	32,7	39,2	36,3	-

As seen from Table. 3, in all Units, except for the renovated station. № 4 and sc the first stage, the cells KRU feeders outgoing connections are dynamically unstable and must be replaced with more powerful with breaking capacity of 31.5 kA. The same applies to the cell, and its switch, and current transformers.

2.3. Testing for thermal stability

Verification data on the thermal resistance of the cells switches switchgear and cable feeders are shown in Table 4.

Table 4. The results of the test circuit switchgear cells o.n. 6 kV and outgoing cables on the thermal resistance

Section o.n. 6 кV	Расчетное B_k, kA			B_kadd.cell, kA²*c	Minimum cable cross – section,
Section o.n. 6 кV	of С	from IM		B_kadd.cell, kA²*c	Minimum cable cross – section,
4 А 5 Б	88,7 81,3	9,1 8,2	97,8 89,5	2976,7 2000	110 105
6 Б 8 Б	74,8 63,9	8,4 7,9	83,2 71,8	2000 2000	101,3 94,1
9 Б 10 Б	55,9 65,6	7,9 9,6	63,8 75,2	2000 2000	88,8 96,4
11 Б 12 Б	71,0 77,1	7,8 8,9	78,8 86,0	2000 2000	98,6 103
13 Б 1 Phase	84,0 53,2	6,6 -	90,6 53,2	2000 2000	105,8 81

As can be seen from Table. 4, cable 3·70мм² cross – sections should be replaced by a large cross section 3·95мм², and even 3·120мм². Thermal resistance as switchgear cells satisfactory.

Conclusion

Based on the short circuit currents after the installation of the boiler and installing a new CBB SRTON showed that most of the equipment that was installed before, does not pass on a valid indicator of inspection:

– breaking capacity circuit breakers cells CRU;

– dynamic stability.

The study was carried out without resistance cables and concretized by the station data.

When writing this abstract the master’s qualification work is notcompleted. Date of final completion of work: December, 2010. Full text of the work and materials on a work theme can be received from the author or his scientific supervisor after that date.

Vasyliev Viacheslav

Electrotechnical faculty

Department of Power Plants

Speciality "Electrical power plants"

Rated short-circuit currents in the system of their own needs 6 kV power of 200 MW SbTES n connection with the installation of unit 4 of the CFB boiler and the changes equipment parameters of their own needs