Channel of series-type magnetohydrodynamic generator

A channel of a series-type magnetohydrodynamic generator comprises a central section with sectionalized electrodes, the ends of the central section adjoining respective transition sections including sectionalized electrodes. Adjacent the free end of each transition section is an end section made as a continuous load electrode. There is a switching element between each pair of the electrodes of the transition sections and between the "outermost electrode of the transition section--load electrode". Connected in parallel with the switching elements are relay and a respective type limit voltage switching elements. Sensitive elements of the same type are inserted between the outermost adjoining sectionalized electrodes of the central and the transition sections.

FIELD OF THE INVENTION 
The invention relates to magnetohydrodynamic (MHD) devices and, more 
particularly, to the channels of series-type MHD generators. 
DESCRIPTION OF THE PRIOR ART 
Known in the art is a channel of a series-type MHD generator, comprising a 
central section with sectionalized electrodes, end sections implemented as 
continuous load electrodes to which a load is connected, and transition 
sections implemented as sectionalized electrodes and located between the 
central section and the end sections. 
The construction described above makes it possible to pick up large 
currents from the channel. However, there result large electric field 
strengths at the joints between the continuous electrodes and the 
sectionalized portion of the channel. 
To reduce the electric field strengths at the joints, use is made of 
properly selected compensation resistors which are inserted between the 
sectionalized electrodes of the transition sections and the continuous 
load electrodes (cf. a paper by W. T. Norris and J. B. Heywood in the 
Proc. IEE, vol. 115, No. 4, April 1968, pp. 555-561). 
Large electric field strengths can be produced, however, when the normal 
operation of the channel is disturbed. 
There is a channel of an MHD generator in which the electric field strength 
is held automatically at a limited value along the entire sectionalized 
portion of the channel (cf. the U.S. Pat. No. 3,940,639 (1976). 
The described construction utilizes switching elements with 
series-connected ballast resistors, which are inserted between each pair 
of adjacent electrodes so as to cancel overvoltages of the same sign as 
that of the channel working voltage. Though the construction uses a 
relatively sophisticated control circuit, there might result, in the zone 
of the joints between the continuous and the sectionalized electrodes, 
large field strengths having a sign opposite that of the channel working 
voltage. Moreover, some power loss place in compensating for the 
differences of the field strengths along the sectionalized portion of the 
channel. 
There is also a channel of a series-type MHD generator, which comprises, 
unlike the construction described above, switching elements inserted each 
between a continuous load electrode and one of the electrodes of the 
transition section (cf. a paper by T. R. Brogan, A. M. Aframe and J. A. 
Hill, MHD Sixth Int. Conf., MHD El. Power Generation, pp. 267-285). There 
are measuring elements, namely, voltmeters, which are connected in 
parallel with the switching elements. The human operator exercises control 
over the switching elements from a control console so as to connect the 
desirable one of the sectionalized electrodes of the transition section to 
the load electrode of the end section. As a result, the joint, which is a 
boundary between the end and the transition portions, is shifted with 
respect to the magnetic system of the MHD generator, with the result that 
the electric field strength at the joint becomes equal to zero. 
The described construction is disadvantageous in that no sequence of 
switching on the electrodes is established, which may cause a disturbance 
in the normal operation of the channel. In addition, a zero electric field 
strength at the joint requires that the electrodes in the transition 
section be sectionalized to a greater extent, which results in a 
sophisticated channel design and complex control functions. It is 
impossible to control and eliminate promptly the overvoltages occurred by 
using a manual control console. 
As a result, breakdowns in the zone of the end section are possible, which 
causes unstable operation of the channel within a wide range of variation 
of the generator parameters, especially in cases when the latter are 
subject to rapid variation. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide for a channel of a series-type MHD 
generator, which offers reliable operation with the generator parameters 
varying within a wide range due to the fact that the electric field 
strength within the channel is maintained in specified limits. 
There is provided a channel of a series-type MHD generator, comprising a 
central section with sectionalized electrodes, the ends of said central 
section being made adjacent a chain of a transition section including 
sectionalized electrodes, and an end section made as a continuous load 
electrode. Switching elements are electrically connected to the electrodes 
of the end and transition sections, the switching elements each being 
connected, according to the invention, between each pair of adjacent 
electrodes. Relay-type limit voltage sensitive elements are each connected 
in parallel with a respective one of said switching elements. Respective 
relay-type limit voltage sensitive elements are inserted between the 
outermost adjacent electrodes of the transition sections and the central 
section. This actuating organs of the sensitive elements, connected in 
parallel with the switching elements between the load electrode and the 
outermost electrode of a respective transition section control the making 
of said corresponding switching elements only; the actuating organs of the 
sensitive elements inserted between the outermost adjacent electrodes of 
the transition sections and the central section to control the breaking of 
the switching elements inserted between the nearest pair of the 
electrodes; and, the actuating organs of the remaining sensitive elements 
control the making of the switching elements in parallel connection with 
them and control the breaking of the switching elements inserted between 
the nearest adjacent pair of the electrodes on the side of the load 
electrode. 
Advantageously, the relay-type limit voltage sensitive elements should be 
voltage polarization relays and the switching elements should be 
automatic-return making retaining contacts. 
The channel of the magnetohydrodynamic generator of the invention is 
characterized by an increased operational reliability, which is attained 
by automatically limiting the electric field strength within the zone of 
the joints to specified limits relating to both positive and negative 
values of the strength. No sophisticated control system is required. In 
addition, the sectionalization pitch of the electrodes is not subject to 
specific limitations. Finally, arcing is not likely to occur.

DETAILED DESCRIPTION OF THE INVENTION 
The channel of the series-type MHD generator comprises, according to the 
invention, a central section 1 (FIG. 1), two end sections 2 each including 
a continuous load electrode 3, and two transition sections 4 each located 
between the central section 1 and a corresponding end section 2. A load 5 
is inserted between the load electrodes 3. The central section 1 includes 
sectionalized electrodes 6 and the transition sections 4 include 
sectionalized electrodes 7. Switching elements 8 are connected between the 
load electrodes 3 and the outermost electrodes 7 of the transition 
sections 4, adjoining the electrodes 3. Switching elements 9 and 10 are 
inserted between adjacent electrodes 7 of the transition sections 4. 
Relay-type limit voltage sensitive elements 11, 12 and 13 are connected in 
parallel with the switching elements 8, 9, 10. In addition, relay-type 
limit voltage sensitive elements 13 are inserted between outermost 
adjacent electrodes 6 and 7 belonging respectively to the central section 
1 and corresponding transition sections 4. The sensitive elements 11 
inserted between the load electrodes 3 and their adjoining sectionalized 
electrodes 7 utilize their actuating organs of direct or indirect action 
to control only those switching elements 8 which are connected between the 
same pairs of the electrodes 3 and 7. The sensitive elements 14 are 
adapted to control the switching elements 10 which are connected to 
adjacent pairs of the electrodes 7 on the side of the load electrodes 3. 
There are dashed lines in FIG. 1 to show control couplings. Each of the 
sensitive elements 12 and 13, for example, that labelled by reference 
numeral 13 and connected to the electrodes 7 of the transition sections 4, 
is adapted to exercise control over either the switching elements 10 
connected to the same electrodes 7 are over the switching elements 9 
connected to adjacent pairs of the electrodes 7 on the side of the load 
electrodes 3. 
One of the simplest embodiments of the circuit diagram of the channel of 
the MHD generator, according to the invention, utilizes polarization 
relays 11' (FIG. 2), 12' and 13', 14' for the limit voltage sensitive 
elements, and making retaining contacts 8', 9' and 10' with automatic 
electromagnetic return for the switching elements. The actuating organ of 
the relay 14' is used to control merely the braking of the contact 10'. 
The actuating organ of the relay 11' operates to control the making of the 
contact 8'. The actuating organ of the relay 12' operates to control the 
making of the contact 9' and the breaking of the contact 8', and the 
actuating organ of the relay 13' is adapted to control the making of the 
contact 10' and the breaking of the contact 9'. 
The electric field strength in the channel of the series-type MHD generator 
of the invention is held within specified limits due to the fact that its 
value and sign, as related to the joint between the load electrode 3 (FIG. 
1) and its adjoining electrode 7 of the transition section 4, depend on 
the position of the joint within the magnetic field of the channel, on the 
mode of operation of the channel, and on the commutation angle, .alpha., 
of the electrodes 7 of the transition section 4. According to FIG. 3, 
point A.sub.1 determines that position of the joint for which all the 
switching elements are held in make state. There is a boundary at which 
induction B begins to drop, shown as a thin vertical line in FIG. 3, with 
distance d.sub.1 separating that boundary from point A.sub.1. Point 
A.sub.2 determines that position of the joint for which all the switching 
elements are held in break state, distance d.sub.2 separating the above 
boundary from point A.sub.2. 
FIG. 4 illustrates a dependence of the electric field strength, E, at a 
given mode of operation of the channel, on the position of the joint 
(distance d), which position being determined by a sequential making of 
the switching elements. According to FIG. 4, there exists a zone of width 
.delta. including different joint positions. In this zone, the absolute 
value of strength E at the joint does not exceed the permissible values of 
strength E.sub.O. FIG. 5 illustrates a dependence of strength E at the 
joint on load coefficient K, which is characteristic of the mode of 
operation of the channel. In FIG. 5, line 15 stands for the position of 
the joint at point A.sub.1 (distance d.sub.1), and line 16 stands for the 
position of the joint at point A.sub.2 (distance d.sub.2). If the absolute 
value of field strength E.sub.1 is less than a permissible value of 
E.sub.O, case when the channel mode is characterized by load coefficient 
K.sub.1, a new value of field strength at the joint, E.sub.1 ', 
corresponding to a load coefficient K.sub.2, exceeds the value of E.sub.O. 
When the position of the joint is transferred from point A.sub.1 (line 15) 
to point A.sub.2 (line 16), the field strength at the joint drops down to 
a value of E.sub.2, which is less than E.sub.O. Flatter curves 
representing a dependence of E on K give greater operational reliability 
and more simple control of the channel. Most favourable control conditions 
are attained with channels whose electrodes 7 of the transition section 4 
have commutation angle .alpha. (FIG. 1), which tends to decrease towards 
the load electrode 3. The associated calculations have been accomplished 
to determine the required channel parameters. With the joint located in a 
zone of a magnetic field having higher values of induction B, for example, 
a position given by point A.sub.1 in FIG. 3, electric field strength 
E.sub.x is distributed along the channel wall, beginning at point A.sub.1, 
as shown in FIG. 6. On the other hand, FIG. 7 shows a distribution of 
electric field strength E.sub.x along the channel wall, beginning at point 
A.sub.2, when the joint is positioned within a zone of a magnetic field 
with lower values of induction B. The analysis of data given by FIGS. 6 
and 7 shows that large overvoltages might occur across the joint and that 
field strength E.sub.x might change its sign. FIGS. 6 and 7 also 
illustrate how potential .tau. across the channel wall changes its 
distribution characteristic. Note that the potential difference between 
the electrodes forming the joint can be given a sign corresponding to or 
opposite that of the rhe channel voltage. 
The channel of the series-type MHD generator of the invention operates in 
the following manner. According to previously made calculations, the 
channel is adjusted with respect to a magnet (not shown) in a manner that 
no impermissible voltage having the same sign as the channel working 
voltage is allowed to be produced across the joints even in most 
unfavourable conditions. If the joint assumes a position at which an 
impermissible voltage of opposite sign occurs across it, the sensitive 
element 11 (FIG. 1) causes the making of the switching element 8 and a 
short circuit condition occurs, including the load electrode 3 and its 
adjoining electrode 7 of the transition section 4. This provides for extra 
strength of the load electrode 3 and a point when it joins the 
sectionalized electrode 7 is transferred to the channel center, with the 
result that the joint voltage is decreased. If, even with this position of 
the joint, an impermissible voltage of opposite sign is produced, the 
sensitive element 12 causes the making of the switching element 9, thereby 
resulting in further shifting of the joint towards the channel center. The 
described events may occur until all the electrodes 7 of the transition 
section 4 are shorted. The boundary between the transition and central 
sections 1 and 4 should be selected by calculation so that no 
impermissible voltage of opposite sign is allowed to appear across the 
joint at that boundary even in most unfavourable conditions. As a result, 
no further shifting of the joint towards the channel center is required in 
this case. The voltage across the joint in this limit position is checked 
by the sensitive element 14. With the joint in the above position, when 
there is an appearance of an impermissible voltage of the same sign as 
that of the channel voltage, the sensitive element 14 operates to break 
the switching element 10, with the result that the joint is transferred 
towards the load electrode 3. The events described may occur until the 
point in time when the switching element 8 breaks and the joint is 
therefore assumes its initial position. 
Thus, the sensitive elements 11-14 are adapted to control the switching 
elements 8-10 so that the electrodes 7 of the transition section 4, on the 
side of the central section 1 of the channel, are opened when direct 
voltage exceeds the permissible level (E.sub.O) and no current overload 
takes place. In addition, automatic shorting of the electrodes 3 and 7 
according to the signals generated by the sensitive elements 11-14 when 
the permissible level of reverse voltage is exceeded eliminates electric 
breakdown of the electrodes. The analysis of electric damage to pilot MHD 
generators shows that almost all causes are concerned with current 
overload and interelectrode breakdown. In the channel of the series-type 
MHD generator of the invention the maximum power of the generator is 
maintained automatically, an important feature unavailable in the known 
competitors.