A semiconverter is a type of power electronic converter that converts AC power to DC power. It consists of a diode rectifier and a thyristor inverter. The rectifier converts the AC input to a pulsating DC voltage, and the inverter converts the pulsating DC voltage to a variable DC output.

Quadrants in power electronics refer to the different combinations of input voltage and current polarities. In total, there are four quadrants: the first quadrant (positive voltage and positive current), the second quadrant (negative voltage and positive current), the third quadrant (negative voltage and negative current), and the fourth quadrant (positive voltage and negative current).

In the case of a semiconverter feeding an RLE (resistor-inductor-capacitor) load, the load is a combination of a resistor, an inductor, and a capacitor. The load can be either a purely resistive load or a combination of resistive, inductive, and capacitive elements. The load impedance determines the power factor and the reactive power consumption of the load.

The semiconverter can operate in different quadrants depending on the load impedance and the firing angle of the thyristor in the inverter. However, in this particular question, it is stated that the semiconverter operates in the first quadrant only.

This means that the semiconverter can only operate with a positive voltage and positive current. In other words, the load impedance must have a positive real part (resistive component) and the current flowing through the load must also be positive. This indicates that the load is primarily resistive and does not have significant reactive power consumption.

The reason for this limitation is that the semiconverter uses thyristors, which are unidirectional devices that can only conduct current in one direction. Thyristors can only be turned on when the voltage across them is positive. Therefore, the semiconverter cannot operate in quadrants where the voltage or current has a negative polarity.

In conclusion, a semiconverter feeding an RLE load operates in the first quadrant only because of the unidirectional nature of thyristors and the requirement for a positive voltage and positive current.