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Metadyne and Amplidyne
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Metadyne and Amplidyne
Metadyne
What is Metadyne ?
Metadyne is a special machine which consists of two pairs of brushes or has an additional set of brushes on the d axis. This arrangement enables the armature MMF to provide most of the excitation and achieve higher power gains. In this, the brushes of the quadrature axis (q axis) are short-circuited, and direct axis (d axis) brushes give the output.
schematic diagram
schematic diagram of a Metadyne
A stator of the machine has a control field winding. A current if flows through the control field winding. The generator is rotating at a constant speed; an EMF eaq is induced between the quadrature axis brushes qq’ because of the control field winding MMF.
how does Metadyne work ?
The brushes qq’ are short-circuited, a quadrature axis armature current iq flows and establish an MMF Fq if the quadrature axis. Since the impedance of the short-circuited path is low, a small change in control field current produces a greater armature current in the q axis.
The magnetic field is stationary in space because of the commutator action. Rotation in the q axis flux produces an EMF in the armature. This EMF appears across the direct axis brushes dd’ 1
If the load resistance RL is connected across the direct axis brushes, the direct axis armature current id will flow through the load. A direct axis flux Fd is produced by this current and according to Lenz’s law, it opposes its main cause, i.e., the control field MMF Ff.
The magnetic field of the current produced is 90 degrees ahead of the flux wave producing the voltage. Since, there are two stages of voltage generation, the MMF of the direct axis output current is shifted twice by 90 degrees. As a result, it opposes the control field MMF.
Amplidyne
what is Amplidyne
Amplidyne is the most common version of the Metadyne. It consists of the basic metadyne in which a compensating winding is connected in series with the power output brush terminals. The compensating winding cancels out the d axis MMF, which opposes the control field MMF.
schematic diagram of the Amplidyne
schematic diagram
The compensating winding is located in the direct (d axis) on the stator. This compensating winding carries the load current id. The winding produces a flux which opposes the flux produced by the direct axis armature current. The effect of the negative feedback of the load current is minimized. The d axis flux now depends on the field winding current.
how does Amplidyne work ?
c
The degree of compensation C is defined as the ratio of effective compensating winding turns to the effective armature turns.