DE102019213866A1 - Regulation of the gas pressure in a generator below atmospheric pressure to increase efficiency - Google Patents

Abstract

In a generator system, the gas pressure is regulated in the negative pressure area to increase efficiency. The gas pressure inside the generator is reduced as much as possible below atmospheric pressure with the aim of reducing the gas-related losses accordingly. The invention implements a needs-based vacuum control for the gas pressure inside the generator / phase shifter during operation. The advantage of the invention lies in the lower gas-related losses of the electrical machine in the case of negative pressure. In the exemplary embodiment, the losses are reduced by around 500kW, which equates to a reduced cooling output corresponding to a monetary benefit of over € 3 million per year.

Description

The invention relates to a method for operating a generator, specifically as a phase shifter, with reduced gas friction losses and thus cooling performance losses.

Losses occur in power plant generators (iron losses, electricity-related losses, gas friction losses through the rotor ball), which make cooling by means of a gas volume flow (e.g. air) necessary. This cooling, on the other hand, contributes directly to lowering the temperatures, but also contributes to the power consumed. The higher this total power loss to be dissipated, the higher the losses caused by the cooling. Another disadvantage here is that the cooling is designed for a maximum case (blade angle of the axial fan, groove base channel and radial slots in the rotor). The gas-related losses (fan, internal pumping of the rotor and ball friction) are of considerable importance. The influence in the phase shifter business is particularly significant, in which every kilowatt of loss corresponds to a monetary disadvantage of € 6,000 per year. In such phase shifter applications, the gas-related losses represent a large part of the total losses of the generator.

In the 1 is based on the example of a conventional generator of the 2000 MW class in phase shifter operation (only reactive power control Q ) shows the proportion of gas-related losses 1 is compared to those of the stand iron 2 , the excitement 3 , and the stator current 4th .

A reduction in friction losses could conventionally be achieved by switching to other cooling gases, such as hydrogen, with an increase in power density associated with this.

The invention is based on the problem of reducing the losses for a generator, in particular in phase shifter operation, while at the same time avoiding inadmissible heating of the machine and maintaining high-voltage boundary conditions, such as, for example, throw distances.

The problem is solved by an object having the features of claim 1.

The inventive step is to create a control for generators / phase shifters, which strives for a gas pressure that is as low as possible (below atmospheric pressure) without accepting inadmissible heating of the machine. In addition to thermal aspects, the logic takes into account C. also structural-mechanical and high-voltage technical boundary conditions.

The invention implements a needs-based vacuum control for the gas pressure inside the generator / phase shifter during operation. According to the invention, the gas pressure inside the generator is reduced as far as possible below atmospheric pressure with the aim of correspondingly reducing the gas-related losses (which are approximately proportional to the density of the cooling gas). Here, the gas pressure is lowered, taking into account the reduced cooling capacity, without leaving the thermal class of the insulation. Furthermore, further circumstances (structural mechanical stability of the housing and minimum gas pressure requirement to guarantee the dielectric strength (breakdown widths) and behavior of the gas cooler at reduced pressure are taken into account. Based on the cold gas temperature T , the current active power W. and reactive power Q (or, for example, their reference variable excitation and stator current) is output from stored control curves that represent the temperatures of the various components, the permitted minimum pressure, but also the minimum pressure. With the help of this value, a vacuum pump is created V via a logical controller C. controlled in such a way that the gas pressure P. inside the generator G adjusts accordingly.

The advantage of the invention lies in the lower gas-related losses of the electrical machine in the case of negative pressure. In the example shown, the losses are reduced by around 500kW, which equates to a reduced cooling effort corresponding to a monetary benefit of over € 3 million per year.

Advantageous further developments of the invention are specified in the subclaims.

• 1 für einen Generator im Phasenschieberbetrieb (nur Blindleistungsregelung), wie hoch der Anteil an gasbedingten Verlusten 1 ist im Vergleich zu denen des Ständereisens 2, der Erregung 3, und des Ständerstromes 4, 2 die gasbedingten Verlustkurven zum Einen konventionell 1 und zum Anderen gemäß der Erfindung 8,
• 3 die Verlustkurven für einen erfindungsgemäßen Generator und
• 4 eine Anordnung eines die Erfindung realisierenden Generators G.

The invention is explained in more detail below as an exemplary embodiment to the extent necessary for understanding with reference to figures. Show:

• 1 for a generator in phase shifter operation (only reactive power control), how high the proportion of gas-related losses 1 is compared to those of the stand iron 2 , the excitement 3 , and the stator current 4th , 2 the gas-related loss curves on the one hand conventional 1 and on the other hand according to the invention 8th ,
• 3 the loss curves for a generator according to the invention and
• 4th an arrangement of a generator realizing the invention G .

In the figures, the same designations denote the same elements.

2 shows the gas-related losses of a commercially available generator in phase shifter operation with different reactive power Q . With the loss curve according to the invention 8th puts on the with M. designated reactive power Q of approx. 100 MVAr, the minimum pressure control to maintain the throw width. The minimum pressure regulation depends on the design and ensures that the distance between the throw distances is maintained.

It should be noted that on the curve 8th (inventive regulation), also in 3 , an impermissibly high temperature is not reached at any point (not even in the stator core).

Gas-related losses have been significantly reduced in wide areas (here: around 700kW, which equates to a monetary difference of over € 4 million per year in the phase shifter business)

Furthermore, the algorithm can be expanded to run low, temporal temperature gradients, if possible. In contrast to known controls, such as a cold gas temperature control, this also has the advantage of low losses at low gas pressures.

1. 1. einer Vakuumpumpe V, die in ihrer Drehzahl zum Beispiel über einen Frequenzumrichter geregelt wird, inklusive einem Sicherheitsventil als Sicherheitseinrichtung für eine untere Druckgrenze,
2. 2. einer statische Druckerfassungseinrichtung P,
3. 3. einem Kaltgastemperatursensor,
4. 4. einer Logik C, welche aus Kaltgastemperatur T, Wirkleistung W und Blindleistung Q einen Mindestdruck errechnet,
5. 5. einem Aktuator, welcher entsprechend die Pumpe V aber auch Ventile ansteuert.

A vacuum system according to the invention can consist of:

1. 1. a vacuum pump V whose speed is regulated, for example via a frequency converter, including a safety valve as a safety device for a lower pressure limit,
2. 2. a static pressure detection device P. ,
3. 3. a cold gas temperature sensor,
4. 4. a logic C. , which from cold gas temperature T , Real power W. and reactive power Q calculates a minimum pressure,
5. 5. an actuator, which accordingly controls the pump V but also controls valves.

A ball valve can be installed in the connection line between the vacuum pump and generator K be arranged for the hydraulic separation of the generator in order to increase the functional safety.

Furthermore, a suitable sealing system is arranged at the interface between the rotor and the housing of the generator, which prevents contamination with outside air. This can be done by using an additional sealing air seal.

The invention can be used both in service with little effort and in new systems.

Instead of the regulation via a frequency converter, which regulates the speed, a control valve can also represent a suitable regulation / control. The nature of the components, for example those of the vacuum pump or those of the valves, is of secondary importance for the realization of the invention.

For purposes of illustration, the present invention has been explained in detail on the basis of specific exemplary embodiments. Elements of the individual exemplary embodiments can also be combined with one another. The invention is therefore not intended to be restricted to individual exemplary embodiments, but rather only to be restricted by the appended claims.

List of reference symbols

1 -

gas-related losses (conventional)

2 -

Stator iron losses

3 -

Loss of excitement

4 -

Loss of stator current

5 -

Loss of the rotor's own production

6 -

Loss of gas friction on the rotor

7 -

Fan losses

8th -

gas-related losses (according to the invention)

C -

Controller, logic

G -

generator

K -

Ball valve for the hydraulic separation of the G

L -

Loss

M -

Minimum pressure regulation

P -

Pressure measurement

Q -

Reactive power

T -

Cold gas temperature

V -

Vacuum pump

W -

Real power

Claims (8)

Method for operating a generator, in particular a phase shifter, for reducing gas friction losses, characterized in that, depending on the operating state, a minimum permissible negative pressure of the gas pressure in the interior of the generator (G) is determined at which the permissible temperature of critical components is not is exceeded and the gas pressure in the interior of the generator is reduced to the determined negative pressure. Procedure according to Claim 1 characterized in that the operating state comprises an optional combination from the group of cooling gas temperature, outside temperature, excitation current, stator current. Method according to one of the preceding claims, characterized in that the operating state is determined by means of a controller C. Method according to one of the preceding claims, characterized in that a vacuum pump is controlled in such a way that the determined gas pressure, in particular negative pressure, is established in the interior of the generator. Method according to one of the preceding claims, characterized in that the vacuum pump is operated via a frequency converter which is controlled in accordance with a signal supplied by the controller. Method according to one of the preceding claims, characterized in that the association between the respective operating state and the minimum permissible negative pressure can be read out from a stored table. Method according to one of the preceding claims, characterized in that the change in the gas pressure in the interior of the generator takes place according to an algorithm which realizes a small temperature gradient due to time. Method according to one of the preceding claims, characterized in that falling below a lower pressure limit is prevented by means of a safety valve.

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