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Re: Safety Thread, NST versus Pole Pigs

Tesla List wrote:
> 
> Original Poster: jim.fosse-at-bjt-dot-net (Jim Fosse)
> 
> On Thu, 10 Sep 1998 22:02:11 -0600, Tesla List <tesla-at-pupman-dot-com>, you
> wrote:
> 
> >Original Poster: Dave Sharpe <sccr4us-at-erols-dot-com>
> 
> [snip]
> >I use
> >INDUSTRIAL SAFETY GUARD LATCH RELAY CIRCUITS, and MULTIPLE E STOPS on my
> >high power equipment and discharge all HV paths. When I operate my
> >equipment, I sit on a INSULATED platform on a wooden floor.
> [snip]
> 
> Dave,
>         Would you care to explain "INDUSTRIAL SAFETY GUARD LATCH RELAY
> CIRCUITS" and "MULTIPLE E STOPS" to us?  I don't have a clue and I are
> {sic} an Electronics Engineer whom is just starting to professionally
> work with 2.6kV -at-(200J 10pps) flash lamp power supplies for lasers.
> 
>         regards,
> 
>         jim

Jim, ALL

Before starting Tesla experimentation 10 years ago, I was responsible
for electrical design of can forming and material handling conveyor
systems (ie, OSHA parlance for pinch, laceration, amputation hazards).
Standard metal working press or machinery practice is to have was
in known as "PROTECTION IN DEPTH", ie one circuit failure will
NOT prevent safety circuits from performing their intended function.

The levels of protection are basically from highest to lowest priority:
1. Main power disconnects:  ALL POWER ISOLATED AND LOCKED OUT AT ONE
   POINT, remote interlock circuits which may be energized by separate
   power sources so marked and isolated.  Usually not a problem with
   Tesla system because remote interlocks "usually" don't exist.
   Only possible exception would be using a large power controller
   to run a smaller auxiluary controller for a large VTTC as an example.
   If a tube fault (overcurrent, flashover, etc.) occurs in
smaller       controller, alarming and system shut down of the powering
controller    (as a remote interlock) would be prudent.
2. Emergency Stop, all rotating/moving components come to controlled
   immediate stop, damage is acceptible, remove all control power
   from field/panel devices.  Force all circuits to open (SAFE)      
condition. Braking devices engaged (if available).  Remove I/O
   power to I/O devices for PLC (programmable logic controllers
or         equivalent), but maintain power on PROCESSOR so system is
maintained    in a known logic condition.
3. Control Power lockout interlocks. Control power is maintained off
   until turned on by an ON-OFF keyswitch that can be locked
out.          Circuit operation impossible without key in switch and on
the ENABLE
   control power to be on.
4. Guard interlocks: Each guard circuit (door, spark gap
vibration,        under speed etc) shall have an independent relay that
is latched        energized when (1) conditions 1,2,3 do not exist, (2)
guard contact     is made (ie condition being alarmed does not exist
[door closed, no     vibration,etc.]) and a reset pushbutton is
depressed.  Latched          energized when circuits are satisfied is
CRITICAL, if a fuse blows,     or power fails, or the inidividual guard
circuit operates, the relay    is de-energized.  Now use a normally
closed contract off each guard     relay to light an annunciation light,
so finding the problem circuit    is easy.  Next wire a normally open
contact from each guard latching    relay in series to a GUARD CLOSED
(OK) relay.  A series contact from    the GUARD CLOSED RELAY powers:
5.  Motor Controls:  Fans, blowers RSG motors and speed controls
    Guard circuits can be employed as 4 for more extensive protection
    of RSG's, (vibration, over/under speed), low air flow etc.
    When all circuits in 5 are satisfied and the RSG is running
    in its proper design envelope and cooling fans are operational then
6.  Main Start-Stop controls. These controls are standard 3 wire        
controlls which operate your main contactor for high power to main     
variacs, ballasts, pole-pigs.  Any overcurrent monitoring, undertrip
    safety circuits are placed in series with control circuit of
main       contactor so that if an OC condition occurs the main
contactor     drops out, de-energizing the load.

DO NOT PLAY GAMES HERE, USE THE LARGEST 600VAC CONTACTOR YOU CAN FIND
100A IS NOT UNDERSIZED; REMEMBER YOUR LIFE MAY DEPEND ON THAT CONTACTOR
RELIABLY DROPPING OUT!!!

Properly over-current protect your equipment, it is not good form for
your main circuit breaker panel to come flying out of the wall because
your new pole pig tried to swallow 1000Amps, and the breaker did just
that; BROKE!

In my control panel, all guard circuits are 12VDC.  If the PS blows
up because of HV kick back, all the guard relays open!!  Fan, RSG
controls are 120VAC (due to higher power requirements).  Main contactor
is 100A, 600V 3ph Allen-Bradley 709 series (ie BULLET-PROOF on 240,1ph).

When operating my system about 5 years ago ALONE, at about 1AM in
morning, the SG across my HV xfmrs flashover while running at about
5kVA. I was startled (gross understatement), and bumped the HV door
which contained above latch relay, limit switch.  System IMMEDIATELY
(less than 100ms) shut down, all fans, RSG stopped, all HV down.
Control power still on, line power indication OK, but the guard
circuit which dominoed the entire panel clearly showed in red it
had done its job.  This one event validated the week of work to wire the
control harness in my panel.  INDUSTRIAL CONTROLS CAN SAVE YOUR AS..;
as well as limit equipment damage if something does go BBUURRAAPPT!!

I also had a preflight procedure for my panel.  This is EXTREMELY
important on high power systems.  CHECK _EVERY_ INTERLOCK AND
CONTROL CIRCUIT; CONFIRM THAT IT WORKS, IF IT DOESN'T, DON'T OPERATE THE
SYSTEM UNTIL IT IS FIXED.  The guard in OSHA parlance is an Engineering
Control, and deliberately defeating a guard device or circuit is a
firing offense in most companies. IF THE CIRCUIT IS DANGEROUS
ENOUGH TO WARRANT A GUARD PROTECTION CIRCUIT, THEN CONFIRM IT
WORKS EACH TIME THE CIRCUIT IS USED; YOUR LIFE MAY DEPEND ON IT.

There is an expression "There are bold pilots, and old pilots, but
no old bold pilots".  Pilots do a preflight of their aircraft,
we should likewise on high power machines; switches do break,
relays can stick, and we all have NEVER HAD COMPONENTS FAIL!
(YEAH, RIGHT ;^) )

Regards

DAVE SHARPE, TCBOR