MIL-DTL-17060G(SH)
For semi-enclosed and open rotor slots:
I1r = 1.04 × I3 × (Vr / V3) σ
where:
σ = 1.05σ2 0.35(σ1 1) for σ2 > σ1
or
σ = 0.7σ2 + 0.35 for σ2 ≤ σ1
and
σ1 = log(I2 / I1) / log(V2 / V1)
σ2 = log(I3 / I2) / log(V3 / V2)
The locked-rotor torque, corrected to rated voltage, shall be the minimum of the three values determined by the
following equation:
T1r = Tm × (Vr / Vm) β
where:
β = log(Tm / Tn) / log(Vm / Vn)
and
m = 3, n = 2; m = 3, n = 1; m = 2, n = 1
To conform to the requirement to lock the rotor for 20 seconds at rated voltage, the rotor shall be locked at
reduced voltage, V3, for a time in seconds determined by the following equation:
tLR = 20 × (Vr × I1r) / (V3 × I3)
The values for the above equations are:
I1r =
locked-rotor current at rated voltage
I3
=
locked-rotor current measured at maximum kVA of test facility
I2
=
measured locked-rotor current intermediate to I3 and I1
I1
=
lowest value of measured locked-rotor current, not less than rated current
Vr =
rated voltage
V3 =
measured locked-rotor voltage at maximum kVA of test facility
V2 =
measured locked-rotor voltage associated with I2
V1 =
measured locked-rotor voltage associated with I1
T1r =
locked-rotor torque at rated voltage
T3 =
measured locked-rotor torque at maximum kVA of test facility
T2 =
measured locked-rotor torque associated with locked-rotor voltage V2
T1 =
measured locked-rotor torque associated with locked-rotor voltage V1
tLR =
period of time, in seconds, with rotor locked at voltage, V3
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