# Math Applications Flashcards

## Wye & Delta, Phase & Line, Power Calculation

The “phase angle” is the angle between _____ and _____

“phase current” and “phase voltage”

Coils in a 3-phase generator are mounted _____ apart from each other

120 mechanical degrees

The sine waves generated by a 3-ohase generator are _____ apart

120 electrical degrees

Phasor diagrams starting at a common point are called _____

Open phasor

Phasor diagrams where second phasor beginning at point where the first ended, are called _____

Tip-to-tail / closed phasor

The length of a phasor represents the _____ value of Voltage

Effective (RMS)

Line voltage in Wye is obtained by measuring _____

Any two lines

Line voltage V(ab) is the _____ sum of _____

Phasoral, V(an) + V(nb)

In a Wye connected load, there is a ____ phase angle between phase and line voltage

30 degrees

(ABC) is _____ phase sequence

Positive

The neutral in a Wye connected load is for what purpose? What would the current in the neutral be in a balanced circuit?

Carries the unbalanced current and maintains equal phase voltage. No current flows in balanced circuit.

If the neutral opens in a wye connection, what happens?

Total supply V applies across both loads. Becomes series circuit.

What is the result of an open neutral in Wye? Where will the highest voltage occur?

Unbalanced phase voltages proportional to the impedance of each phase. Highest V across largest impedance.

The unbalanced current in Wye will be the _____ sum of the _____

Phasor, three line currents

I(b) being 240 degrees from reference phasor I(a), it is located in a quadrant making the horizontal and vertical components _____

Negative

I(c) being 120 degrees from reference phasor I(a), located in the quadrant making the horizontal and vertical components _____

Horizontal = negative, Vertical = positive

In a balanced Wye load with a lagging power factor, line current and voltage are out of phase by _____

30 degrees plus phase angle

Phase and line voltage in Wye is _____

30 degrees out of phase

The relationship between line and phase current in Wye is _____

They are equal

The angle between line current and voltage in Wye at unity pf is _____

30 degrees

In Delta, the relationship between E(line) and E(phase) is _____

They are equal.

How would you confirm the correct connection of a 3-phase Delta transformer secondary? What would reversing the leads on a coil do?

Open corner test - Voltmeter shows 0 V.

Reversing would show voltmeter reading of twice the phase voltage.