Two challenges need to be addressed in designing active network management (ANM) for
distribution networks that use non-firm connection agreements for quicker and cheaper connections of
distributed energy resource (DER). First is the replacement of scripted actions based on priority lists by
real-time selection of actions offered as ancillary services and judged on efficacy and cost. Second is the
need to decentralize or distribute ANM decision making to avoid unrealistic communication and computation
burdens as the number of controllable devices increases. This paper proposes a distributed form of ANM
for radial networks, based on local estimation of the voltage sensitivities to offered adjustments of real or
reactive power and then uses message passing between local controllers to arrive at near-optimum choices
of actions. To manage a voltage constraint, the minimum volume (or cost) of ancillary services is found by
selecting services from DERs with highest voltage sensitivity to the service offered. A method of sensitivity
estimation for individual nodes is extended to all terms of the inverted Jacobian matrix. The accuracy of this
approximation is discussed and explored in a case-study network. The format of message passing from one
local controller to another is described. Simulations demonstrate that the proposed distributed ANM closely
approaches the solution found by a centralized optimal power flow. It is confirmed that the use of locally
estimated voltage sensitivity to identify the most effective DER can minimize the volume of power flow
adjustment service that the ANM needs to manage voltage and thermal constraints.