JVC KD-SV3204UI Service Manual page 17

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τ ： Heat time constant, reflecting motor overload capability
This criterion fully considers the thermal process and thermal status before overload of motor stator. The device
would use thermal capacity to represent motor thermal process, and thermal capacity is proportional to the square
of stator current.
Through conversion, its dimension is turned to be time constant τ, reflecting motor overload capability. When the
value of thermal capacity reaches τ, the device would trip. When thermal capacity reaches K
sent. Thereinto, K is alarm coefficient, with value range:
a
Overheat alarm could be set as (60 ～ 9 9.9) ％ of overheat trip thermal capacity value. The device would
provide real-time thermal capacity percentage display, alarm light indicator and signal contact output. The
overheat alarm function could be controlled through control character KG1.0. When overheat alarm function
operates, no matter whether overheat protection soft jumper is operating, the alarm would function.
During motor operation, heat dissipation time constant is the same as heat time constant τ. After motor
shutdown, the dissipation effect is getting worse. The lower cooling capability of motor makes dissipation time
constant longer than heat time constant τ, dissipation time constant would automatically increase to be certain
times of heat time constant τ, in order to correctly reflect heat effect. The times of dissipation time could be
selected form 1 to 5, and the default tacitly approved value is 4 times, according to real environment condition.
According to the principle that motor could start for continuous two times, and the percentage of each startup
thermal capacity should not be larger than 50% of trip value, so when thermal capacity percentage descends to
below 50%, device closing blocking contact returns. After overheat protection trip, the function of overheat
holding starts, and output contact would always be closed, until thermal capacity percentage descending to below
50%, the overheat closing blocking contact would return, and the motor could restart at this time. In case of
emergency, when immediate startup is required, press " ＜ " key and " ＞ " key on device panel at the same time,
and carry out overheat reset operation according to cues. This overheat blocking function could be controlled
through control character KG1.1, and its output is the standby output 4( 6 X : 1 5 ～ 6 X : 1 6 ) .
Heat time constant τ should be provided by motor manufactory, if the manufactory dose not offer this, it
could be estimated using one of the following methods:
If the manufactory provides motor thermal limit curve or a group of overload capability data, τ could be
①
computed according to following formula:
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×τ, overheat alarm is
a
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