The primary mmf is least affected by the secondary terminal conditions in a current transformer.

Explanation:
A current transformer (CT) is a type of transformer that is used to measure electric current. It is designed to step down the current flowing through a conductor to a lower value that can be easily measured and monitored.

When current flows through the primary winding of a CT, it produces a magnetic field that induces a current in the secondary winding. The primary mmf (magnetomotive force) is the magnetic field created by the primary winding, and it is directly proportional to the primary current.

The primary mmf is least affected by the secondary terminal conditions in a current transformer due to the following reasons:

1. Turns Ratio: The turns ratio of a current transformer is very high, usually ranging from 100:1 to 5000:1. This means that for a given primary current, the secondary current is significantly smaller. As a result, the secondary load impedance has minimal effect on the primary mmf.

2. Low Secondary Voltage: The secondary voltage of a CT is typically very low, usually around a few volts. This low voltage ensures that the secondary load impedance has minimal effect on the primary mmf.

3. Negligible Secondary Current: In an ideal current transformer, the secondary current is ideally zero when the primary current is zero. This means that even if there is a short circuit or open circuit on the secondary side, it will not affect the primary mmf.

4. High Magnetizing Impedance: The primary winding of a current transformer has a high magnetizing impedance, which limits the flow of magnetizing current. This further ensures that the primary mmf is least affected by the secondary terminal conditions.

Overall, the primary mmf of a current transformer is least affected by the secondary terminal conditions due to the high turns ratio, low secondary voltage, negligible secondary current, and high magnetizing impedance. This makes the current transformer an ideal device for accurately measuring electric current without significantly affecting the primary circuit.