JPH0122972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Description of the technical field The present invention relates to a single-phase autotransformer with a tertiary winding.

(b) Description of the prior art Direct grounding systems are used in Japan's ultra-high voltage power transmission systems of 187KV to 275KV and above, and the transformers used to connect these systems are subject to Japan's strict railway transportation restrictions. To accommodate this, a single-phase autotransformer is used.

Figure 1 shows the wiring diagram of a typical conventional single-phase single-winding transformer, with series winding 1, shunt winding 2,
Tap windings 4 are connected in series, one end of which is used as a high-voltage line terminal U, the other end used as a neutral point terminal v, and a tertiary winding 3 is provided, the terminals of which are used as tertiary terminals a and b, and this tertiary winding 3 and an excitation winding 5 that excites the tap winding 4 are connected in parallel, and the series winding 1
The voltage at the low-voltage line terminal U, which is the connection point between the line and the separation winding 2, is kept constant, and the voltage at the high-voltage line terminal U is varied.

An example of a specific configuration of this single-phase autotransformer is shown in FIGS. 2 and 3. FIGS. 2a and 2b show a conventional single-phase three-legged core, in which a is a front view showing the arrangement of core punching, and FIG. 2b is a plan view showing a cross section of each core leg. As can be seen from Fig. 2, a single-phase three-legged core generally consists of two pairs of single-phase two-legged cores 71 and 72 having the same cross-sectional area, adjacent to each other in the longitudinal direction. The iron core legs on both sides were used as side legs. The cross-sectional area of the central leg therefore has twice the cross-sectional area of the side legs.

Figure 3 is a front view showing the single-phase autotransformer in which each winding is arranged on the single-phase tripod core shown in Figure 2.
A series winding 1, a shunt winding 2 and a tertiary winding 3 are wound on the center side, and a tap winding 4 and an excitation winding 5 connected in parallel to the tertiary winding 3 are wound on one side leg. has been done. The configuration shown in Figure 3 has the advantage that the voltage of the excitation winding 5 is generally the same as the tertiary voltage, which is a low voltage, and the winding configuration is relatively simple. Go to the high voltage line end U
Since the voltage of the tap is varied, the excitation of the iron core changes depending on the tap position, which has the disadvantage that the tertiary voltage fluctuates. For example, actually used
In the case of a 500KV/√3-275KV/√3-63KV single-phase single-turn transformer with tertiary winding, the core excitation voltage ratio at each of the highest tap, rated tap, and lowest tap is
252.7KV (=527.7−275): 225KV (=500−225):
It is 202.7KV (=477.7−275). Therefore, the tertiary voltage is 70.8KV, 63KV, 56.8KV at each tap.
and fluctuates significantly. The tertiary terminals a and b are generally delta-connected in a three-phase bank, and a capacitor or reactor is connected to adjust the reactive power. Therefore, if the terminal voltage changes significantly depending on the tap position as described above, the utilization rate of the capacitor etc. will decrease. This causes problems such as a decrease in power consumption and complicated reactive power control.

Furthermore, the tertiary winding capacity is generally about 20 to 30% of the primary and secondary capacity, which is smaller than other main windings (series windings and shunt windings). In the example, since these are wound around the same core leg, the impedance between the tertiary winding and other windings, especially the impedance between the secondary (low voltage) primary and tertiary windings, tends to become too small. If this tertiary impedance is small, the fault current in the event of a tertiary external short circuit will be large, so the tertiary winding must have a larger capacity than is thermally necessary to withstand the large electromagnetic mechanical force caused by the fault current. become. Also, if the fault current in the tertiary circuit is large,
The tertiary circuit and disconnector also require a larger capacity. Therefore, the larger the capacitance is, the more effective it is to increase the tertiary impedance, but for this reason, increasing the distance between the tertiary winding and other windings beyond the distance required for insulation will increase the size of the entire transformer. However, there are limitations due to transportation restrictions and economic efficiency. There is also a plan to provide a current limiting reactor in the tertiary circuit, but this would complicate the configuration and be disadvantageous from an economic point of view.

However, on the other hand, if the impedance between the tertiary winding and the other windings connected in delta in a three-phase bank becomes too large, the zero-sequence impedance of the transformer seen from the secondary will become large in the primary region.
This makes it unsuitable as a transformer for use in a directly grounded system. That is, in a directly grounded system, it is desired to suppress the rise in ground voltage of a healthy phase as low as possible even in the event of a line-to-ground fault in the system, and to do so, it is necessary to reduce the zero-sequence impedance of the system.

In a three-phase bank that combines three single-phase single-winding transformers, the impedance between the delta-connected tertiary winding and other windings becomes the zero-sequence impedance, so as mentioned above, the impedance of the tertiary winding From the standpoint of cubic capacity, it is better to have a larger value, but if it is too large, it will cause problems in system operation.

(c) Purpose of the Invention The present invention provides an improved single-phase autotransformer that eliminates the drawbacks of the conventional single-phase autotransformer and allows the tertiary impedance to be selected at an appropriate value. The purpose is to

(d) Embodiment of the Invention An embodiment of the present invention will be described below with reference to the drawings. Figure 4 shows a single-phase tripod core used in a single-phase autotransformer according to the present invention, where a is a front view showing the arrangement of core punching, and b is a plan view showing a cross section of each core leg. be. In FIG. 4, two sets of single-phase bipedal cores 81 and 82 adjacent to each other in the longitudinal direction have different cross-sectional areas, but the sum of them, that is, the cross-section of the central leg that combines the adjacent core legs. The area is the same as the cross-sectional area of the central leg in the conventional example shown in FIG.

FIG. 5 shows a front view of a single-phase autotransformer according to the present invention in which each winding is arranged on the single-phase tripod core shown in FIG. 4, and FIG. 6 shows its wiring diagram. In other words, the series winding 1 and the shunt winding 2 are connected to the center leg of the single-phase tripod core.
and a tap winding 4, and a tertiary winding 3 and a low voltage winding 6 are wound around the side leg with a larger cross-sectional area, and both ends of the low voltage winding 6 are connected to the low voltage line terminal u.
and is connected to the neutral point v.

With this configuration, the tertiary winding 3 is excited by the low voltage winding 6 whose voltage is kept constant, so the voltage does not fluctuate depending on the position of the tap in the tap winding 4. There is no. Furthermore, since the tertiary winding 3 is wound around the side legs whose cross-sectional area is smaller than the center leg, the number of windings is equal to the cross-sectional area ratio a (=center leg cross-sectional area/ As a result, the inter-winding impedance, that is, the tertiary impedance, becomes approximately ^twice as large as the side leg cross-sectional area). Therefore, for example, if the cross-sectional area of the side legs with a small cross-sectional area is selected to be 30% of the center leg, and the cross-sectional area of the side legs with a large cross-sectional area is selected to be 70% of the center leg, the tertiary impedance will be approximately 2 because a = 1/0.7. It becomes twice (=1/0.72). Similarly, if a=1/0.58 is chosen, it can be approximately tripled. When the conventional example shown in Fig. 2 has the same configuration, a = 1/0.5, and the tertiary impedance becomes approximately four times. There is much more flexibility in impedance magnitude. Therefore, it is possible to adjust the tertiary impedance appropriately.

Next, FIGS. 7 and 8 show a front view and a wiring diagram of a single-phase autotransformer according to another embodiment of the present invention. This single-phase autotransformer has a series winding 1 and a shunt winding 2 wound around the central leg of the single-phase tripod core shown in Figure 4, and a tertiary winding 3 wound around the side leg with a larger cross-sectional area. A low voltage winding 6 is wound thereon, and both ends of the low voltage winding 6 are connected to a low voltage line terminal u and a neutral point v.

Further, a tap winding 4 and an excitation winding 5 are wound around an iron core 83 different from the single-phase tripod iron core, and the excitation winding 5 is connected in parallel with the tertiary winding 3.

When configured in this way, not only can the same effect as the embodiment shown in FIG. If the tap part is stored in a separate tank from the transformer body, in the unlikely event of an accident involving the tap part, by disconnecting it, the transformer body can continue operating as a transformer without a tap. Furthermore, this tap portion can be combined with other two phases to form a three-phase device, and in this case there is a great advantage that a three-phase star connection neutral point switching tap changer can be used effectively.

(e) Effects of the Invention As explained above, the present invention provides an improved single-phase autotransformer in which the tertiary voltage does not vary depending on the tap position and the tertiary impedance can be appropriately adjusted. Obtainable.

[Brief explanation of drawings]

Figure 1 is a wiring diagram of a conventional tertiary winding single-phase single-winding transformer, and Figures 2 a and b show a front view showing the arrangement of core punching in a conventional single-phase three-legged core, and a cross-section of each core leg. A plan view, FIG. 3 is a front view of a single-phase autotransformer using the core shown in FIG. 2 and the wiring shown in FIG. 1, and FIGS. FIG. 5 is a front view showing the arrangement of core punching of a single-phase three-legged core and a plan view showing a cross section of each core leg; FIG. 5 is a front view showing a single-phase autotransformer according to the present invention; FIG. Winding wiring diagram shown in figure 7
The figure is a front view showing another embodiment of the single-phase autotransformer of the present invention, and FIG. 8 is a wiring diagram of the winding shown in FIG. 7. 1...Series winding, 2...Shunt winding, 3...Tertiary winding,
4... Tap winding, 5... Excitation winding, 6... Low voltage winding,
71, 72, 81, 82...single phase biped core, 83...
Iron core, U...High voltage line terminal, u...Low voltage line terminal, v
...neutral point terminal, a, b...tertiary terminal.

Claims (1)

[Claims] 1. Two sets of single-phase bipedal cores with different cross-sectional areas of the core legs are placed adjacent to each other, the adjacent core legs are combined to form a central leg, and the core legs located on both sides are used as side legs to form a single-phase core. A series winding, a shunt winding, and
A tap winding is wound, and a tertiary winding and a low voltage winding are wound around one side leg having a large cross-sectional area, and one end of the low voltage winding is connected to the connection point between the series winding and the shunt winding. A single-phase single-winding transformer, characterized in that the other end is connected to a low-voltage line terminal, and the other end is connected to a neutral point terminal drawn out through the tap winding. 2. Two sets of single-phase two-legged cores with different cross-sectional areas of the core legs are placed adjacent to each other, the adjacent core legs are combined to form a central leg, and the core legs located on both sides are used as side legs to form a single-phase three-legged core, A series winding and a shunt winding connected in series are wound around the central leg of this single-phase tripod core, and a tertiary winding and a low voltage winding are wound around one of the side legs having a large cross-sectional area. A tap winding connected in series to the shunt winding and an excitation winding connected in parallel to the tertiary winding are wound around an iron core other than the single-phase tripod iron core, and the low voltage winding has one end thereof. A single-phase single-winding transformer, characterized in that the other end is connected to a low voltage line terminal serving as a connection point between the series winding and the shunt winding, and a neutral point terminal drawn out via the tap winding.