Angle from caster to orb.
So let's save everything into variables:
array unit variable - OrbUnit[]
array real variable - OrbAngle[]
When you cast the spell, you'll set
OrbUnit[1] = first orb
OrbUnit[2] = second orb
OrbUnit[3] = third orb
And
OrbAngle[1] = 0
OrbAngle[2] = 120
OrbAngle[3] = 240
Every loop of the spell, you
move OrbUnit[x] to position of caster offset by 300 towards OrbAngle[x]
and then set OrbAngle[x] = OrbAngle[x] + 10 (adjust the 10 for whatever speed you want)
NB: when OrbAngle[x] goes over 360, set it to OrbAngle[x] - 360, things can go funny when angles go above 360.